Method and apparatus for transmitting and receiving data using a plurality of carriers in mobile communication system

ABSTRACT

A bearer reconfiguration method performed by a User Equipment (UE) in a wireless communication system supporting a multi-bearer is provided. The bearer reconfiguration method includes, if the UE performs a bearer reconfiguration from a single bearer to the multi-bearer, reordering Packet Data Convergence Protocol (PDCP) Protocol Data Units (PDUs) received through the multi-bearer, using a timer after a completion of the bearer reconfiguration, and processing the reordered PDCP PDUs into at least one PDCP Service Data Unit (SDU). The method may also include, if the UE performs bearer reconfiguration from the multi-bearer to the single bearer, reordering PDCP PDUs received through the multi-bearer, using a timer until a predetermined condition is satisfied, and processing the reordered PDCP PDUs into at least one PDCP SDU.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 U.S.C. § 119(a) of a Koreanpatent application filed on Jan. 29, 2014 in the Korean IntellectualProperty Office and assigned Serial number 10-2014-0011775, a Koreanpatent application filed on Feb. 10, 2014 in the Korean IntellectualProperty Office and assigned Serial number 10-2014-0014890, a Koreanpatent application filed on Mar. 21, 2014 in the Korean IntellectualProperty Office and assigned Serial number 10-2014-0033716, a Koreanpatent application filed on Mar. 31, 2014 in the Korean IntellectualProperty Office and assigned Serial number 10-2014-0038265, a Koreanpatent application filed on Jun. 9, 2014 in the Korean IntellectualProperty Office and assigned Serial number 10-2014-0069127, a Koreanpatent application filed on Jul. 1, 2014 in the Korean IntellectualProperty Office and assigned Serial number 10-2014-0082139, a Koreanpatent application filed on Jul. 18, 2014 in the Korean IntellectualProperty Office and assigned Serial number 10-2014-0091164, and a Koreanpatent application filed on Sep. 26, 2014 in the Korean IntellectualProperty Office and assigned Serial number 10-2014-0129620, the entiredisclosure of each of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a method and apparatus fortransmitting and receiving data using a plurality of carriers in amobile communication system.

BACKGROUND

Mobile communication systems have been developed to providecommunication services while ensuring a user's mobility. Recently, themobile communication systems have reached a stage capable of providingnot only the voice communication services but also the high-speed datacommunication services.

In recent years, a Long Term Evolution (LTE) system proposed by the 3rdGeneration Partnership Project (3GPP) is providing its services in manycountries as one of the next-generation mobile communication systems.The LTE system is technology for implementing high-speed packet-basedcommunication having a transfer rate of about 100 Mbps.

To meet the demand for wireless data traffic having increased sincedeployment of 4G (4th-Generation) communication systems such as the LTEsystem, efforts have been made to develop an improved 5G(5th-Generation) or pre-5G communication system. Therefore, the 5G orpre-5G communication system is also called a ‘Beyond 4G Network’ or a‘Post LTE System’.

The 5G communication system is considered to be implemented in higherfrequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higherdata rates. To decrease propagation loss of the radio waves and increasethe transmission distance, the beamforming, massive multiple-inputmultiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna,an analog beam forming, large scale antenna techniques are discussed in5G communication systems.

In addition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud RadioAccess Networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, Coordinated Multi-Points (CoMP), reception-endinterference cancellation and the like.

In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and slidingwindow superposition coding (SWSC) as an advanced coding modulation(ACM), and filter bank multi carrier (FBMC), non-orthogonal multipleaccess (NOMA), and sparse code multiple access (SCMA) as an advancedaccess technology have been developed.

Recently, the commercialization of an LTE-Advanced (LTE-A) communicationsystem that has improved its transfer rate by combining a variety of newtechnologies for the LTE communication system is underway. The mosttypical one of the technologies to be newly introduced may includeCarrier Aggregation (CA). The term ‘carrier aggregation’ as used hereinmay refer to technology in which one terminal or User Equipment (UE)uses a plurality of forward carriers and a plurality of reverse carriersin transmitting and receiving data, unlike the technology according tothe related art in which a UE transmits and receives data using oneforward carrier and one reverse carrier.

Currently, however, only the intra-Evolved Node B (ENB) CA is defined inLTE-A. This may result in reducing the applicability of the CA function,thus causing the possible problems that macro cells and pico cellscannot be aggregated especially in a scenario where a plurality of picocells and one macro cell are operated in an overlapping manner. The picocell may be referred to as another term such as ‘micro cell’, ‘smallcell’ or the like.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present disclosure.

SUMMARY

Aspects of the present disclosure are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentdisclosure is to provide a method and apparatus for efficientlytransmitting and receiving data using a plurality of carriers in amobile communication system.

Another aspect of the present disclosure is to provide a method andapparatus for inter-Evolved Node B (ENB) carrier aggregation (CA).

Another aspect of the present disclosure is to provide a method andapparatus for Packet Data Convergence Protocol (PDCP) operationswitching in a mobile communication system supporting multi-bearer.

Another aspect of the present disclosure is to provide a method andapparatus for PDCP reordering in a mobile communication systemsupporting multi-bearer.

In accordance with an aspect of the present disclosure, a bearerreconfiguration method performed by a User Equipment (UE) in a wirelesscommunication system supporting a multi-bearer is provided. The bearerreconfiguration method includes, if the UE performs a bearerreconfiguration from a single bearer to the multi-bearer, reorderingPDCP Protocol Data Units (PDUs) received through the multi-bearer, usinga timer after a completion of the bearer reconfiguration, and processingthe reordered PDCP PDUs into at least one PDCP Service Data Unit (SDU).

In accordance with another aspect of the present disclosure, a bearerreconfiguration method performed by a UE in a wireless communicationsystem supporting a multi-bearer is provided. The bearer reconfigurationmethod includes, if the UE performs a bearer reconfiguration from themulti-bearer to a single bearer, reordering PDCP PDUs received throughthe multi-bearer, using a timer until a predetermined condition issatisfied, processing the reordered PDCP PDUs into at least one PDCPSDU.

In accordance with another aspect of the present disclosure, a UE in awireless communication system supporting a multi-bearer is provided. TheUE includes a receiver configured to receive data and a controllerconfigured to, reorder PDCP PDUs received through a multi-bearer, usinga timer after a completion of the bearer reconfiguration if the UEperforms a bearer reconfiguration from a single bearer to themulti-bearer, and process the reordered PDCP PDUs into at least one PDCPSDU.

In accordance with another aspect of the present disclosure, a UE in awireless communication system supporting a multi-bearer is provided. TheUE includes a receiver configured to receive data and a controllerconfigured to, reorder PDCP PDUs received through a multi-bearer, usinga timer until a predetermined condition is satisfied if the UE performsa bearer reconfiguration from the multi-bearer to a single bearer andprocess the reordered PDCP PDUs into at least one PDCP SDU.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 illustrates a structure of a Long Term Evolution (LTE) systemaccording to an embodiment of the present disclosure;

FIG. 2 illustrates a radio protocol structure in an LTE system accordingto an embodiment of the present disclosure;

FIG. 3 illustrates an intra-Evolved Node B (ENB) carrier aggregation(CA) in an LTE system according to an embodiment of the presentdisclosure;

FIG. 4 illustrates an inter-ENB CA in an LTE system according to anembodiment of the present disclosure;

FIG. 5 illustrates a connection structure of a Packet Data ConvergenceProtocol (PDCP) device in an LTE system according to an embodiment ofthe present disclosure;

FIG. 6 illustrates a PDCP operation switching process in an LTE systemaccording to an embodiment of the present disclosure;

FIG. 7 illustrates a reconfiguration of a Radio Link Control (RLC)device during a PDCP operation switching process in an LTE systemaccording to an embodiment of the present disclosure;

FIG. 8 illustrates an operation of a User Equipment (UE) during a bearerreconfiguration in an LTE system according to an embodiment of thepresent disclosure;

FIG. 9 illustrates an upper layer delivery condition of a PDCP operationin an LTE system according to an embodiment of the present disclosure;

FIG. 10 illustrates an operation of a PDCP reception device in an LTEsystem according to an embodiment of the present disclosure;

FIG. 11 illustrates an operation performed when a timer 1 expires in thePDCP reception device as illustrated in FIG. 10 according to anembodiment of the present disclosure;

FIG. 12 illustrates a UE's operation of setting a Prioritized Bit Rate(PBR) for a multi-bearer according to an embodiment of the presentdisclosure;

FIG. 13 illustrates a format of a status PDU according to an embodimentof the present disclosure;

FIG. 14 illustrates an operation of an RLC reception device generating astatus Protocol Data Unit (PDU) according to an embodiment of thepresent disclosure;

FIG. 15 illustrates an operation of an RLC transmission device receivinga status PDU according to an embodiment of the present disclosure;

FIG. 16 is a block diagram illustrating a configuration of a UE in anLTE system according to an embodiment of the present disclosure;

FIG. 17 is a block diagram illustrating a configuration of an ENB in anLTE system according to an embodiment of the present disclosure;

FIG. 18 illustrates an ENB's operation of performing downlink datatransmission/reception with a UE that has reported three categoriesaccording to an embodiment of the present disclosure;

FIG. 19 illustrates a UE operation according to an embodiment of thepresent disclosure;

FIGS. 20, 24, 28, and 29 illustrate various examples of a UE operationduring a bearer reconfiguration according to various embodiments of thepresent disclosure;

FIG. 21 illustrates an operation of a PDCP reception device operatingwith a multi-bearer according to an embodiment of the presentdisclosure;

FIG. 22 illustrates an operation of a PDCP reception device thatswitches to a PDCP operation 5 when reconfiguring a bearer from amulti-bearer into a Master Cell Group (MCG) bearer according to anembodiment of the present disclosure;

FIG. 23 illustrates an operation of a PDCP reception device performedwhen a timer 3 expires according to an embodiment of the presentdisclosure;

FIG. 25 illustrates a PDCP operation 7 of a PDCP reception deviceoperating with a multi-bearer according to an embodiment of the presentdisclosure;

FIG. 26 illustrates an operation of a PDCP reception device performedwhen a timer 3 expires according to an embodiment of the presentdisclosure; and

FIG. 27 illustrates an operation of determining whether a UE hasreceived, in duplicate, a PDCP PDU according to an embodiment of thepresent disclosure.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the present disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thepresent disclosure. In addition, descriptions of well-known functionsand constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of the presentdisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of the presentdisclosure is provided for illustration purpose only and not for thepurpose of limiting the present disclosure as defined by the appendedclaims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

Descriptions of some well-known technologies that possibly obscure thedisclosure will be omitted, if necessary. The disclosure now will bedescribed more fully hereinafter with reference to the accompanyingdrawings, in which illustrative embodiments of the disclosure are shown.Prior to a description of the present disclosure, the Long TermEvolution (LTE) system and carrier aggregation (CA) will be described inbrief. In various embodiments of the present disclosure, the LTE systemmay be construed to include an LTE-Advanced (LTE-A) system.

FIG. 1 illustrates a structure of an LTE system according to anembodiment of the present disclosure.

Referring to FIG. 1, a Radio Access Network (RAN) of an LTE system mayinclude Evolved Node Bs (ENBs) (or Node Bs or base stations) 105, 110,115 and 120, a Mobility Management Entity (MME) 125 and aServing-Gateway (S-GW) 130. A User Equipment (UE) (or a terminal) 135may access an external network (not shown) through the ENBs 105, 110,115 and 120 and the S-GW 130.

The ENBs 105, 110, 115 and 120 may correspond to the legacy Node B inthe Universal Mobile Telecommunication System (UMTS) system. The ENBs105, 110, 115 and 120 may be connected with the UE 135 over a wirelesschannel, and may perform a more complex role than the legacy Node B. Inthe LTE system, since all user traffic including real-time services suchas Voice over Internet Protocol (VoIP) is serviced over a sharedchannel, there is a need for a device that performs scheduling bycollecting status information such as buffer status, availabletransmission power status and channel status of UEs, and the schedulingis managed by the ENBs 105, 110, 115 and 120. Each of the ENBs 105, 110,115 and 120 may usually control a plurality of cells. For example, inorder to implement a transfer rate of 100 Mbps, the LTE system may usean Orthogonal Frequency Division Multiplexing (OFDM) scheme in a 20-MHzbandwidth as its radio access technology. In addition, the ENBs 105,110, 115 and 120 may use an Adaptive Modulation & Coding (AMC) schemefor adaptively determining a modulation scheme and a channel coding rateaccording to the channel status of the UE 135. The S-GW 130, which is adevice that provides data bearers, may create or remove a data bearerunder control of the MME 125. The MME 125, which is responsible not onlyfor the mobility management function for the UE 135 but also for avariety of control functions, may be connected to a plurality of ENBs.

FIG. 2 illustrates a radio protocol structure in an LTE system accordingto an embodiment of the present disclosure.

Referring to FIG. 2, in a radio protocol structure of the LTE system, aUE and an ENB may include Packet Data Convergence Protocols (PDCPs) 205and 240, Radio Link Controls (RLCs) 210 and 235, and Medium AccessControls (MACs) 215 and 230, respectively.

The PDCPs 205 and 240 are responsible for operations such as InternetProtocol (IP) header compression/decompression, and the RLCs 210 and 235may reconstruct PDCP Protocol Data Units (PDUs) in a proper size toperform an Automatic Repeat reQuest (ARQ) operation. The MACs 215 and230, which are connected to multiple RLC layer devices configured in oneUE, may perform an operation of multiplexing RLC PDUs in a MAC PDU, anddemultiplexing RLC PDUs from a MAC PDU. Physical layers (PHY) 220 and225 may channel-code and modulate upper layer data to make OFDM symbols,and transmit them over a wireless channel, and the physical layers 220and 225 may demodulate and channel-decode OFDM symbols received over awireless channel, and deliver them to their upper layers.

FIG. 3 illustrates an intra-ENB CA in an LTE system according to anembodiment of the present disclosure.

Referring to FIG. 3, one ENB may generally transmit and receive multiplecarriers over a plurality of frequency bands. For example, when acarrier 315 with a forward center frequency f1 and a carrier 310 with aforward center frequency f3 are transmitted from an ENB 305, one UE maytransmit and receive data using any one of the two carriers f1 and f3,according to the related art. However, a UE 330 having the CA capabilitymay transmit and receive data over multiple carriers at the same time.The ENB 305 may allocate more carriers to the UE 330 having the CAcapability depending on the situation, thereby increasing a transferrate of the UE 330. This approach of aggregating a forward (or downlink)carrier and a reverse (or uplink) carrier that one ENB transmits andreceives may be referred to as intra-ENB CA. However, in some cases,there may be a need to aggregate downlink carriers and uplink carriersthat are transmitted and received from/at different ENBs, unlike in theexample shown in FIG. 3.

FIG. 4 illustrates an inter-ENB CA in an LTE system according to anembodiment of the present disclosure.

Referring to FIG. 4, when an ENB1 405 transmits and receives data over acarrier with a center frequency f1 and an ENB2 415 transmits andreceives data over a carrier with a center frequency f2, a UE 430 mayaggregate (or combine) the carrier with a downlink center frequency f1and the carrier with a downlink center frequency f2, leading to theresults that one UE aggregates carriers from two or more ENBs. Herein,this will be referred to as inter-ENB CA. In this specification,inter-ENB CA will be referred to as Dual Connectivity (DC), and forexample, the expression that DC is set may refer to the expression thatinter-ENB CA is set; the expression that one or more cell groups areset; the expression that a Secondary Cell Group (SCG) is set; theexpression that at least one secondary serving cell (SCell), which iscontrolled by another ENB other than the serving ENB (SeNB), is set; theexpression that a primary serving cell (PCell or pSCell) is set; theexpression that a MAC entity for an SeNB is set; and the expression thattwo MAC entities are set in a UE.

The terms used herein will be described below.

In the traditional sense, when one downlink carrier that one ENBtransmits and one uplink carrier that the ENB receives constitute onecell, ‘carrier aggregation’ may be construed as an operation in which aUE transmits and receives data through multiple cells at the same time.In this case, the maximum transfer rate and the number of carriersaggregated may have a positive correlation.

Herein, the expression that a UE receives data over any downlink carrieror transmits data over any uplink carrier has the same meaning as theexpression that the UE transmits and receives data using a controlchannel and a data channel that are provided by a cell corresponding toa center frequency and a frequency band characterizing the carrier.Herein, CA will be expressed as ‘a plurality of serving cells is set’,and the terms such as a PCell and an SCell or an enabled serving cellwill be used. These terms may have the same meanings as those used inthe LTE mobile communication system. In the present disclosure, theterms such as a carrier, a component carrier and a serving cell will beinterchangeably used.

Herein, a set of serving cells controlled by the same ENB will bedefined as a Cell Group or a Carrier Group (CG). A cell group may bedivided again into a Master Cell Group (MCG) and a Secondary Cell Group(SCG). MCG refers to a set of serving cells controlled by an ENB (e.g.,a master ENB (MeNB)) that controls the PCell, and SCG refers to a set ofserving cells controlled by an ENB (e.g., a slave ENB (SeNB)) thatcontrols only the ENBs (e.g., SCells) other than the ENB controlling thePCell. As to information about whether a serving cell belongs to an MCGor an SCG, an ENB provides the information to a UE in a process ofsetting the serving cell. One MCG and one or more SCGs may be set forone UE. Although it will be assumed herein that one SCG is set forconvenience purpose only, details of the present disclosure may beapplied as it is, even though one or more SCGs are set. The PCell andSCell are the terms indicating the type of the serving cell, which isset for a UE. There are some differences between the PCell and theSCell. For example, while the PCell keeps an active status at all times,the SCell may alternate between an active status and an inactive statusunder instruction of the ENB. The UE's mobility may be controlled on thebasis of the PCell, and the SCell may be construed as an additionalserving cell for data transmission/reception. The PCell and SCell hereinmay refer to a PCell and an SCell, which are defined in the LTE standardTS36.331 or TS36.321 proposed by the 3rd Generation Partnership Project(3GPP).

In the present disclosure, macro cells and pico cells will beconsidered. A macro cell, which is a cell controlled by a macro ENB, mayprovide services in a relatively large area. On the other hand, a picocell, which is a cell controlled by an SeNB, may provide services in anarea that is significantly narrower compared with the typical macrocell. Although there are no strict criteria for distinguishing betweenthe macro cell and the pico cell, it may be assumed that for example, anarea of the macro cell may have a radius of about 500 meters and an areaof the pico cell may have a radius of about tens of meters. Herein, thepico cell and the small cell will be interchangeably used.

Referring to FIG. 4, if the ENB1 405 is an MeNB and the ENB2 415 is anSeNB, a serving cell 410 with a center frequency f1 may be a servingcell belonging to an MCG and a serving cell 420 with a center frequencyf2 may be a serving cell belonging to an SCG.

In the following description, other terms instead of MCG and SCG may beused for better understanding. For example, terms such as a master setand a secondary set, or a primary carrier group and a secondary carriergroup may be used. However, in this case, it should be noted that thoughthe terms are different, their meanings are the same. The main purposeof these terms is to determine whether a certain cell is controlled byan ENB that controls a PCell of a particular UE, and the operating modeof the UE and the cell may vary depending on whether or not the cell iscontrolled by the ENB that controls the PCell of the particular UE.

Although one or more SCGs can be set for a UE, it will be assumed hereinthat a maximum of one SCG is set for convenience purpose only. An SCGmay include a plurality of SCells, any one of which may have a specialattribute.

In the typical intra-ENB CA, a UE may transmit not only a Hybrid ARQ(HARQ) feedback and Channel Status Information (CSI) for a PCell butalso an HARQ feedback and CSI for an SCell, over a Physical UplinkControl Channel (PUCCH) of the PCell. This is to apply CA even to a UEincapable of simultaneous uplink transmission.

In the case of inter-ENB CA, it may be impossible in reality to transmitan HARQ feedback and CSI of CSG SCells over a PUCCH which is an uplinkcontrol channel of the PCell. The HARQ feedback should be deliveredwithin an HARQ Round Trip Time (RTT) (commonly 8 ms), since thetransmission delay between the MeNB and the SeNB may be longer than theHARQ RTT. Because of these problems, PUCCH transmission resources may beset in one of the SCells belonging to an SCG, and an HARQ feedback andCSI for SCG SCells may be transmitted over the PUCCH. The special SCellwill be referred to as a pSCell. In the following description, theinter-ENB CA will be interchangeably used with the DC.

Generally, one user service may be serviced by one Evolved Packet System(EPS) bearer, and one EPS bearer may be connected with one radio bearer.A radio bearer may be configured with PDCP and RLC, and in inter-ENB CA,it is possible to increase the data transmission/reception efficiency bydisposing a PDCP device and an RLC device of one radio bearer ondifferent ENBs. In this case, different approaches are needed dependingon the type of the user service.

FIG. 5 illustrates a connection structure of a PDCP device in an LTEsystem according to an embodiment of the present disclosure.

Referring to FIG. 5, in the case of, for example, a high-capacity dataservice, a user service may transmit and receive data to/from both of anMeNB and an SeNB by forming two RLC devices as shown by referencenumeral 510. If the user service is a service with strict Quality ofService (QoS) requirements like Voice over LTE (VoLTE), the user servicemay transmit and receive data using only the serving cell of the MeNB bydisposing an RLC device only on the MeNB as shown by reference numeral505. Hereinafter, for convenience of description, a bearer 505 will bereferred to as a single bearer, and a bearer 510 will be referred to asa multi-bearer. A PDCP device of a single bearer may be connected withone RLC device, and a PDCP device of a multi-bearer may be connectedwith two RLC devices. An RLC device (which is connected with a MACdevice associated with serving cells of an MCG) from/at which data istransmitted and received through an MCG will be referred to as an MCGRLC 515, and an RLC device from/at which data is transmitted andreceived through an SCG will be referred to as an SCG RLC 520. A MAC 525associated with data transmission/reception through the MCG will bereferred to as MCG-MAC, and a MAC 530 associated with datatransmission/reception through the SCG will be referred to as anSCG-MAC. The MAC and RLC devices may be interconnected by a logicalchannel. A logical channel between the MCG RLC and the MCG-MAC will bereferred to as an MCG logical channel, and a logical channel between theSCG RLC and the SCG-MAC will be referred to as an SCG logical channel.

Hereinafter, for convenience of description, a macro-cell area refers toan area where no small-cell signal is received and only the macro-cellsignal is received, and a small-cell area refers to an area where amacro-cell signal is received and a small-cell signal are receivedtogether. When a UE with a large demand for downlink data has moved fromthe macro-cell area to the small-cell area, a small cell may beadditionally set for the UE, and a bearer having a large amount ofdownlink data like a File Transfer Protocol (FTP) among some bearers ofthe UE may be reconfigured from a single bearer to a multi-bearer. Inother words, when a UE moves from a macro-cell area to a small-cellarea, and back to the macro-cell area, a certain bearer may bereconfigured from a single bearer to a multi-bearer, and back into thesingle bearer. Since a PDCP device of a single bearer is connected withone RLC and the RLC delivers in-sequence (or ordered) packets to thePDCP, the PDCP device may process the packets delivered by the RLC inorder. On the other hand, a PDCP device of a multi-bearer may beconnected with two RLCs, and each RLC may deliver in-sequence packets.However, since packets may not be in sequence (or may be out ofsequence) between the RLC devices, the PDCP device may process thepackets after ordering them. Therefore, as for the PDCP device, when thebearer is reconfigured from a single bearer to a multi-bearer, orreconfigured from a multi-bearer to a single bearer, an operationperformed by the PDCP device may also be changed at a proper time.

In an embodiment of the present disclosure, an operation of a UE may bedivided into a PDCP operation 1, a PDCP operation 2 and a PDCP operation3.

The PDCP operation 1 is an operation that is applied to a PDCP of asingle bearer. Details of the above operation follow Section 5.1.2 ofthe 3GPP standard TS36.323. The PDCP operation 2 is another operationthat is applied to the PDCP of the single bearer, and the PDCP operation1 is applied in the general case.

The PDCP operation 2 may be applied in an exceptional case where a lowerlayer device cannot perform reordering (e.g., during a handoversituation or a Radio Resource Control (RRC) connection reestablishmentprocedure). Details of the above operation also follow Section 5.1.2 ofthe 3GPP standard TS36.323. When operating in the PDCP operation 1, thePDCP may perform the necessary process under the assumption that theorder of the received packets is correct, and then deliver to, an upperlayer, the received packet and packets having lower sequence number thanthat of the received packet. On the other hand, in a case where a lowerlayer device does not perform reordering, since the order of receivedpackets may not be correct in, for example, the PDCP operation 2, thePDCP may store the packets in a reordering buffer without deliveringthen to the upper layer. Thereafter, at the time the lower layer deviceprovides again the reordering (e.g., if the handover is completed or theRRC connection reestablishment procedure is completed), the PDCP mayswitch to the PDCP operation 1, and the stored PDCP Service Data Units(SDUs) may be delivered to the upper layer together with the newlyreceived PDCP SDUs. Switching between the PDCP operation 1 and the PDCPoperation 2 may occur immediately the moment the PDCP receives, forexample, a control message for instructing a handover, and the PDCPoperation 2 may be applied for a short time right after the handover hasoccurred. In an embodiment of the present disclosure, the PDCP operation3 is newly introduced.

The PDCP operation 3, which is an operation that is applied to a PDCP ofa multi-bearer, has been designed to be used in a situation where twoRLC devices connected with the PDCP device receive PDCP PDUs, and PDCPPDUs received from one RLC device are in sequence (or ordered), whereasPDCP PDUs received from different RLC devices are not in sequence (orare out of sequence). In the PDCP operation 1 and the PDCP operation 2,the PDCP may first process the received PDCP PDUs into PDCP SDUs, andthen determine whether they are reordered. On the other hand, in thePDCP operation 3, the PDCP may first determine whether the received PDCPPDUs are reordered, and then process only the in-sequence PDCP PDUs intoPDCP SDUs and deliver them to the upper layer. Even in the PDCPoperation 3, the PDCP may process PDCP PDUs into PDCP SDUs, and thenperform reordering. Details of the PDCP operation 1, the PDCP operation2, and the PDCP operation 3 will be described below. As described above,while the PDCP operation 2 may be temporarily applied in the handoversituation, the PDCP operation 3 may be continuously applied while thePDCP is operating with a multi-bearer. In a single bearer, the PDCPoperation 1 may be applied, and in a multi-bearer, the PDCP operation 3may be applied. When an arbitrary bearer is switched from a singlebearer to a multi-bearer or vice versa, the PDCP may switch a PDCPoperation from the PDCP operation 1 to the PDCP operation 3, or from thePDCP operation 3 to the PDCP operation 1. If the operation switching ismade in an early time, an unnecessary delay may occur when the PDCPdevice delivers data to the upper layer device. If the operationswitching is made in a late time, data loss may occur.

FIG. 6 illustrates a PDCP operation switching process in an LTE systemaccording to an embodiment of the present disclosure.

Referring to FIG. 6, operations of a UE and an ENB, which are associatedwith bearer reconfiguration including a process in which the UE performsthe PDCP operation switching at a proper time, will be described indetail.

Referring to FIG. 6, in a mobile communication system including a UE605, an MeNB 610 and an SeNB 615, the MeNB 610 may determine to add aserving cell of the SeNB 615 to the UE 605 at an arbitrary time andperform a procedure for serving cell addition with the SeNB 615 inoperation 620. If the MeNB 610 first sets an SCell of the SeNB 615 forthe UE 605 (e.g., if the MeNB 610 sets a first SCG SCell), the MeNB 610and the SeNB 615 may determine which bearer the MeNB 610 will serviceand which bearer the SeNB 615 will service. The MeNB 610 and the SeNB615 may reconfigure a bearer (e.g., a bearer requiring high-speed datatransmission on a downlink) which meets the predetermined condition,into a multi-bearer. Hereinafter, for convenience of description, itwill be assumed that a bearer x is reconfigured from a single bearer toa multi-bearer.

In operation 625, the MeNB 610 may send a predetermined RRC controlmessage to the UE 605. The RRC control message may contain SCellconfiguration information and multi-bearer information. The SCellconfiguration information is for the newly added SCell, and may alsoinclude information indicating whether the SCell is an MCG SCell or anSCG SCell. The multi-bearer configuration information is informationabout a radio bearer that is reconfigured from a single bearer to amulti-bearer, and may include an identifier of the radio bearer and SCGRLC configuration information.

In operation 630, upon receiving the control message, the UE 605 maygenerate an SCG RLC device for a bearer indicated by a beareridentifier, to connect it with a PDCP device, and may connect the SCGRLC device to a MAC device for an SCG. The UE 605 may switch from thePDCP operation 1 to the PDCP operation 3 at the time the configurationof the multi-bearer is completed or at the time the below-describedrandom access is completed. The existing RLC device (e.g., the MCG RLC)of the bearer may perform a normal data transmission/reception operationeven during the reconfiguration process (e.g., an operation ofdelivering the in-sequence PDCP PDUs to the PDCP device, and storing theout-of-sequence (or unordered) PDCP PDUs in an RLC buffer to make anattempt to recover the missing PDUs through an ARQ process. As will bedescribed below, unlike in the reconfiguration process from a singlebearer to a multi-bearer, in a reconfiguration process from amulti-bearer to a single bearer, the MCG RLC device may also stop theRLC reception operation, and then perform the RLC reconfigurationprocess.

In operation 635, the UE 605 may perform random access in the newlyadded SCG SCell. Through the random access procedure, the UE 605 mayestablish uplink synchronization with the newly added SCG SCell and setthe uplink transmission power. If the random access procedure iscompleted, the UE 605 may switch an operation of the PDCP device that isreconfigured to the multi-bearer, from the PDCP operation 1 to the PDCPoperation 3 in operation 640. The time the random access procedure iscompleted may include the time the UE receives a valid random accessresponse message in a case where a dedicated preamble is used, and thetime the UE receives an uplink grant or a downlink assignment, which isaddressed to a Cell-Radio Network Temporary Identifier (C-RNTI) andindicates new transmission, in a case where a random preamble is used.Other details related to the random access follow the LTE standardTS36.321.

In operation 645, the UE 605 may send a predetermined RRC controlmessage to the MeNB 610 to report the completion of the SCellconfiguration and multi-bearer reconfiguration. In operation 650, uponreceiving the reported information, the MeNB 610 may forward downlinkdata of the multi-bearer to the SeNB 615, and the SeNB 615 may initiatetransmission of the downlink data to the UE 605 through the SCG RLC ofthe multi-bearer.

In operation 655, the UE 605 may send the RRC control message, and thenreceive the downlink data of the multi-bearer from the MCG RLC deviceand the SCG RLC device, and apply the PDCP operation 3 for the receivedPDCP PDUs.

Thereafter, in operation 670, the MeNB 610 or the SeNB 615 may determineto release the SCG SCell at an arbitrary time. After performing theprocedure for releasing the SCG SCell, the MeNB 610 or the SeNB 615 maysend an RRC control message to the UE 605 to instruct release of the SCGSCell in operation 675.

In operation 680, upon receiving the control message, the UE 605 mayrelease the SCG SCell in response to the instruction. If the controlmessage indicates the release of the last SCG SCell (e.g., if the UE 605releases the SCG SCell in response to the instruction of the controlmessage), the UE 605 may perform the procedure necessary forreconfiguration from a multi-bearer to a single bearer even though thereis no more SCG SCell or there is no separate instruction. The UE 605 mayperform an operation for reconfiguration from a multi-bearer to a singlebearer similarly, even if the control message explicitly indicates thereconfiguration from a multi-bearer to a single bearer.

Reconfiguration Operation from Multi-Bearer to Single Bearer:

-   -   1) Release an indicated SCG RLC of a multi-bearer;    -   2) Reconfigure an indicated MCG RLC reception device of a        multi-bearer;    -   3) Discard downlink HARQ buffer data of MCG-MAC; and    -   4) Trigger a PDCP status report.

In the process of releasing the SCG RLC, the UE 605 may reconfigure thedownlink RLC PDUs stored in the SCG RLC into RLC SDUs, and then deliverthem to the PDCP, and may discard the uplink RLC PDUs and downlink RLCSDUs stored in the SCG RLC. The RLC SDUs/PDCP PDUs delivered from theSCG RLC are out-of-sequence RLC SDUs/PDCP PDUs (i.e., there are RLC SDUsthat have not been received yet even though they were transmittedearlier than the RLC SDUs).

The expression that a UE reconfigures an MCG RLC reception device mayrefer to an expression that the UE initializes a reception window,initializes a reception sequence number, delivers to the PDCP thedownlink RLC PDUs that can be reconfigured into RLC SDUs, among thedownlink RLC PDUs stored in its reception buffer, and discards theremaining downlink RLC PDUs. The UE may not discard the uplink RLC PDUsand RLC SDUs stored in its transmission buffer.

A PDCP status report may be triggered for each radio bearer, and the UE605 may check a sequence number of a PDCP packet stored in its buffer ofthe PDCP of the bearer that is reconfigured from a multi-bearer to asingle bearer, to generate a PDCP status report including informationassociated with a sequence number of a missing PDCP packet. The PDCPbuffer may store therein the PDCP PDUs delivered from the SCG RLC, andthe PDCP PDUs delivered from the MCG RLC.

The PDCP status report is control information that is used to preventthe loss of the PDCP packet in the handover or RRC connectionreestablishment procedure. The handover or RRC connectionreestablishment procedure may accompany reestablishment (e.g.,reestablishment of a lower layer from the perspective of the PDCPdevice) of all RLC devices configured in the UE 605. If the handover orRRC connection reestablishment procedure is initiated, the UE 605 maytrigger the PDCP status report for all Data Radio Bearers (DRBs) thatsatisfy the following PDCP status report generation condition 1. If thelast SCG SCell is released, the UE 605 may trigger the PDCP statusreport for all DRBs satisfying the following PDCP status reportgeneration condition 2. If a bearer is reconfigured from a multi-bearerto a single bearer, the UE 605 may check whether the bearer satisfiesthe following PDCP status report generation condition 3, to determinewhether to generate a PDCP status report.

PDCP status report generation condition 1:

-   -   A DRB in which statusReportRequired is set, among the DRBs in        which an RLC Acknowledgement Mode (AM) is set.

PDCP status report generation condition 2:

-   -   A multi-bearer among the DRBs in which the RLC AM and the        statusReportRequired are set.

PDCP status report generation condition 3:

-   -   At least one of the SCG RLC and MCG RLC of the multi-bearer        operates in RLC AM.

The statusReportRequired follows the description in the standardsTS36.331 and TS36.323.

If the UE 605 reconfigures the multi-bearer into the single bearer, theUE 605 may switch the operation of the PDCP of the reconfigured bearerfrom the PDCP operation 3 to the PDCP operation 2 in operation 685. ThePDCP may store therein the out-of-sequence PDCP SDUs delivered from theMCG RLC, and the out-of-sequence PDCP SDUs delivered from the SCG RLC.The PDCP may store the PDCP SDUs delivered in the reconfigurationprocess of the MCG RLC and the PDCP SDUs delivered in the releaseprocess of the SCG RLC in its PDCP buffer in the order of COUNT,generate a PDCP status report in which both of the reception status ofthe PDCP SDUs delivered from the MCG RLC and the reception status of thePDCP SDUs delivered from the SCG RLC are reflected, and transmit thePDCP status report to the MeNB 610.

In operation 690, the UE 605 may send a predetermined RRC controlmessage to the MeNB 610 to report the successful completion of the aboveprocedure, and the UE 605 and the MeNB 610 may exchange uplink data anddownlink data with each other through the MCG SCells.

Especially in the reconfiguration process from a multi-bearer to asingle bearer, the UE may not only release the SCG RLC device, but alsoreconfigure the MCG RLC device. In principle, the MCG RLC device is notaffected in the reconfiguration process from a multi-bearer to a singlebearer, so it is not necessary to reconfigure the MCG RLC device.

However, in an embodiment of the present disclosure, the MCG RLC devicemay be artificially reconfigured in order to make efficient switching ofthe PDCP operation as shown in the example of FIG. 7.

FIG. 7 illustrates a reconfiguration of an RLC device during a PDCPoperation switching process in an LTE system according to an embodimentof the present disclosure.

Referring to FIG. 7, at the time the reconfiguration from, for example,a multi-bearer to a single bearer is instructed, out-of-sequence PDCPPDU [10] and PDCP PDU [11] may be stored in an MCG RLC 710 (i.e., a PDCPPDU [9] is missing), and out-of-sequence PDCP PDU [7], PDCP PDU [8],PDCP PDU [12], PDCP PDU [13] and PDCP PDU [14] may be stored in an SCGRLC 715. For reference, it will be assumed that a front number of arectangle represents an RLC sequence number. For example, an RLCsequence number of the PDCP PDU [10] is 5, and an RLC sequence number ofthe PDCP PDU [11] is 6. If only the SCG RLC delivers PDCP PDUs when thereconfiguration from a multi-bearer to a single bearer is instructed, itmay be difficult for the PDCP 705 to determine whether the packetsfollowing the PDCP PDU [12] are reordered, until the PDCP PDUs [10] and[11] are delivered from the MCG RLC, so another reordering operationshould be introduced. In an embodiment of the present disclosure, inorder to solve the above problems, if the reconfiguration from amulti-bearer to a single bearer is made, reconfiguration may be appliedeven for the MCG RLC device so that all the PDCP SDUs that are out ofsequence at that time may be stored in the PDCP buffer.

In addition, the PDCP may first apply the PDCP operation 2 withoutimmediately operating the PDCP operation 1 so that the out-of-sequencePDCP SDUs may not be immediately delivered to the upper layer. In otherwords, the UE may release the SCG RLC device and reconfigure the MCG RLCdevice, and then switch the PDCP operation from the PDCP operation 3 tothe PDCP operation 2. If a first PDCP PDU is received after the beareris reconfigured into a single bearer, the PDCP may switch from the PDCPoperation 2 to the PDCP operation 1.

FIG. 8 illustrates an operation of a UE during a bearer reconfigurationin an LTE system according to an embodiment of the present disclosure.In the example of FIG. 8, a UE's operation of reconfiguring an arbitrarybearer x from a normal bearer to a multi-bearer and back to the normalbearer will be described.

Referring to FIG. 8, in operation 805, a UE may apply the PDCP operation1 for a bearer x which is a single bearer. In operation 810, the UE mayreceive a control message for reconfiguring the bearer x into amulti-bearer. In operation 815, the UE may generate/configure an SCG RLCdevice to be connected with the multi-bearer depending on theconfiguration information indicated by the control message, and thenconnect the SCG RLC device with the PDCP. In operation 820, the UE mayswitch the PDCP operation from the PDCP operation 1 to the PDCPoperation 3. In other words, the UE may check whether PDCP PDUs arereordered, beginning at the PDCP PDU that is first received after thebearer is reconfigured into a multi-bearer, and then apply the PDCPoperation 3 for determining whether to deliver the PDCP PDUs to theupper layer. Thereafter, by applying the PDCP operation 3 for the PDCPPDUs of the reconfigured bearer, the UE may perform an operation ofconverting the PDCP PDUs into PDCP SDUs, and delivering the in-sequencePDCP SDUs to the upper layer.

Upon receiving a control message for instructing to reconfigure themulti-bearer into a single bearer in operation 825, the UE may releasethe SCG RLC and reestablish the MCG RLC in operation 830. In this case,the UE may release both of the transmission device and the receptiondevice for the SCG RLC, and reestablish only the reception device forthe MCG RLC. In other words, the UE may normally process the RLC SDUsand RLC PDUs stored in the MCG RLC transmission device withoutdiscarding them, and may assemble, as RLC SDUs, all the RLC PDUs thatcan be assembled in RLC SDUs, among the RLC PDUs stored in the RLCreception device, and then deliver them to the PDCP and discard theremaining RLC PDUs.

In operation 835, the UE may first switch the PDCP operation to the PDCPoperation 2, without immediately switching the PDCP operation from thePDCP operation 3 to the PDCP operation 1. In other words, the UE mayconvert PDCP PDUs delivered from the MCG RLC and SCG RLC into PDCP SDUsby processing the PDCP PDUs according to the COUNT, and then store allthe SDUs following the first missing SDU in the buffer.

In operation 840, the UE may apply the PDCP operation 1 for the PDCPPDUs, beginning at the PDCP PDU that is first received after the beareris reestablished into a single bearer. In other words, after the UEconverts the first PDCP PDU into an SDU, even though there is a missingSDU among the SDUs with COUNT that is lower than COUNT of the receivedSDU, the UE may deliver the SDUs whose COUNTs are consecutive aroundthat of the received SDU, to the upper layer, determining that the SDUsare in sequence.

Operations 830, 835, and 840 may be modified as follows. The UE mayrelease the SCG RLC and keep the MCG RLC in operation 830, and mayswitch the PDCP operation from the PDCP operation 3 to the PDCPoperation 2 in operation 835. In other words, the UE may process thePDCP PDUs delivered from the SCG RLC, and store the out-of-sequence PDCPSDUs in the PDCP buffer without delivering them to the upper layer. Inoperation 840, if the switching to a single bearer is completed, or if afirst PDCP PDU is received after the switching to the single bearer, theUE may start a predetermined timer 2. The UE may keep the PDCP operation2 while the timer 2 is in operation, and may switch from the PDCPoperation 2 to the PDCP operation 1 if the timer 2 expires. In otherwords, while the timer 2 is in operation, the UE may wait until theout-of-sequence PDCP PDUs which have occurred due to the release of theSCG RLC are in sequence. The timer 2 should be set to a time that islong enough so that the out-of-sequence reception may be resolved. Asfor values of a timer 1 and a timer 2, the ENB may notify the values tothe UE using a predetermined RRC control message.

As for the PDCP operation 1, the PDCP operation 2 and the PDCP operation3, it may be understood that multiple detailed operations that should beapplied for the PDCP PDUs delivered from the RLC device are listed in aseries of order. Detailed operations constituting these operations andthe order thereof are listed in Table 1 below. The following detailedoperations may be conducted in the order from top to bottom.

TABLE 1 PDCP operation 1 PDCP operation 2 PDCP operation 3 PDCP PDUreception PDCP PDU reception PDCP PDU reception Determine HFN/ DetermineHFN/ Determine HFN/ COUNT of PDCP COUNT of PDCP COUNT of PDCP PDU.Discard PDU. Discard PDU. Discard PDU if it PDU if it PDU if it isreceived is received is received in duplicate. in duplicate. induplicate. Process PDCP PDU Process PDCP PDU Process PDCP PDU into PDCPSDU into PDCP SDU into PDCP SDU Deliver the PDCP Deliver PDCP Store PDCPSDU and PDCP SDUs satisfying SDU in the SDUs satisfying upper layer PDCPbuffer. upper layer delivery Deliver PDCP delivery condition 2 to SDUssatisfying condition 1 to the upper layer. upper layer delivery theupper layer. Store the re- condition 3 to the Store the re- maining SDUsin upper layer. Store maining SDUs in the PDCP buffer. the remainingSDUs the buffer. in the PDCP buffer.

How to determine Hyper Frame Number (HFN)/COUNT of a received PDCP PDU,which is given in Table 1, will be described below. COUNT is a 32-bitinteger, and may increase one by one, starting at zero (0). One COUNTmay be granted per PDCP packet, and may be used for a security-relatedoperation such as ciphering/deciphering of a PDCP packet. COUNT maymonotonically increase in the order in which a PDCP packet is deliveredto a lower layer, and in principle, COUNT may assigned in the order inwhich a PDCP SDU is delivered from an upper layer. COUNT may beconfigured with (or may include) HFN and PDCP Sequence Number (SN).While PDCP SN may be transmitted by being included in a header of a PDCPpacket, HFN may not be explicitly delivered. Therefore, a PDCP receptiondevice should determine HFN of a received packet on its own. If a PDCPtransmission device complies with a predetermined condition (e.g., acondition that a packet is transmitted so that the out-of-sequence ofPDCP SN may be less than a half of the total of sequence numbers thatcan be indicated by PDCP SN) in transmitting a packet, the PDCPreception device may determine HFN, using the sequence number (receivedPDCP SN; see the standard 36.323) of the last received PDCP packet, thehighest sequence number (Next_PDCP_RX_SN; see the standard 36.323) amongthe sequence numbers that have been received so far, the window with apredetermined size (Reordering_Window; see the standard 36.323), and thehighest sequence number (Last_Submitted_PDCP_RX_SN; see standard 36.323)among the sequence numbers that have been delivered to the upper layerso far. If a packet with a sequence number higher than that of thereceived packet is already delivered to the upper layer (e.g., if thereceived packet has already been received, or is a delayed receivedpacket), the PDCP reception device may perform header decompression onthe received packet, and then discard the received packet. In moredetail, when a packet is received in duplicate, or is received with adelay for some reasons that cannot be specified, the PDCP receptiondevice may perform header decompression on the packet, and then discardit, since the packet may contain useful information for update of headerdecompression context. The process of determining the HFN may follow thedescription in Section 5.1.2.1.2 of the standard 36.323.

Processing a PDCP PDU whose HFN and COUNT are determined, into a PDCPSDU may refer to deciphering a PDCP PDU and decompressing a header of anIP packet contained in the PDCP PDU, and details thereof may follow thedescription in the standard 36.323.

Hereinafter, for convenience of description, COUNT corresponding toLast_Submitted_PDCP_RX_SN will be referred to asLast_Submitted_PDCP_RX_COUNT, COUNT corresponding to received PDCP SNwill be referred to as received PDCP COUNT, and COUNT corresponding toNext_PDCP_RX_SN will be referred to as Next_PDCP_RX_COUNT. It will beassumed that Last_Submitted_PDCP_RX_COUNT is the highest COUNT (e.g.,the in-sequence highest COUNT) delivered to the upper layer, receivedPDCP COUNT is COUNT of the received PDCP packet, and Next_PDCP_RX_COUNTis a value obtained by adding one (1) to the highest COUNT among theCOUNTs that have been received so far.

An upper layer delivery condition 1 of the PDCP operation 1 is asfollows.

Upper Layer Delivery Condition 1 of PDCP Operation 1

If processing for an arbitrary PDCP SDU [X] is completed in the PDCPoperation 1, the UE may determine that ‘SDUs with COUNT lower than X’and ‘SDUs with COUNT lower than the lowest missing COUNT among themissing COUNTs greater than X’, among the PDCP SDUs stored in thebuffer, have satisfied the upper layer delivery condition 1, and thendeliver the SDUs to the upper layer. For example, if PDCP SDU [90]˜PDCPSDU [99], PDCP SDU [101]˜PDCP SDU [110], and PDCP [112]˜PDCP [115] werestored in the PDCP buffer when PDCP SDU [100] is received, then PDCP SDU[100], PDCP SDU [90]˜PDCP SDU [100] which are PDCP SDU with COUNT lowerthan that of PDCP SDU [100], and PDCP SDU [101]˜PDCP SDU [110] which arePDCP SDUs preceding PDCP SDU[111] which is the first missing PDCP SDUamong the PDCP SDUs with COUNT higher than that of PDCP SDU [100] may bedelivered to the upper layer as they satisfy the upper layer deliverycondition 1, and PDCP SDU[112]˜PDCP SDU [115] may be kept being storedin the buffer. In the PDCP operation 1 that is triggered by receiving anarbitrary PDCP PDU, received PDCP SDUs may be unconditionally deliveredto the upper layer, and in addition, PDCP SDUs satisfying the upperlayer delivery condition 1 may also be delivered to the upper layer.

An upper layer delivery condition 2 of the PDCP operation 2 is asfollows.

Upper Layer Delivery Condition 2 of PDCP Operation 2

In the PDCP operation 2 that is triggered by receiving an arbitrary PDCPPDU, if the received PDCP SDU is a missing PDCP SDU with the lowestCOUNT (e.g., if Received PDCP COUNT is the same as a value obtained byadding 1 to Last_Submitted_PDCP_RX_COUNT), the next missing PDCP SDUsincluding the received PDCP SDU may be delivered to the upper layer. Ifthe received PDCP SDU is not the missing PDCP SDU with the lowest COUNT,the PDCP SDU may be stored in the PDCP buffer. In the PDCP operation 3that is triggered by receiving an arbitrary PDCP PDU, it is checkedwhether there are SDUs satisfying an upper layer delivery condition 3among the PDCP SDUs stored in the PDCP buffer, including the processedPDCP SDU, and only the SDUs satisfying the upper layer deliverycondition 3 may be delivered to the upper layer.

The upper layer delivery condition 3 of the PDCP operation 3 will bedescribed below.

Upper Layer Delivery Condition 3 of PDCP Operation 3

FIG. 9 illustrates an upper layer delivery condition of a PDCP operationin an LTE system according to an embodiment of the present disclosure.

Referring to FIG. 9, in a single bearer 905 in which one logical channelis set up, a PDCP transmission device 910 may deliver packets to an RLCreception device 915 in the order of packet [1], packet [2], packet [3]and packet [4]. The packets may be received at an RLC transmissiondevice 920 through a MAC device and a wireless channel. In this case, ifan error occurs in the wireless channel, retransmission/error recoverymay be conducted using HARQ and ARQ, so the order of packets that theRLC transmission device 920 receives in this process may be differentfrom the order of packets that the PDCP transmission device 910 hastransmitted. The RLC transmission device 920 may reorder theout-of-sequence packets, and then deliver the packets to a PDCPreception device 925. For example, the RLC transmission device 920 maydeliver packets to the PDCP reception device 925 in the order of packet[1], packet [2], packet [3] and packet [4].

In the case of a multi-bearer 930 in which two logical channels are setup, a PDCP transmission device 935 may deliver packets to two RLCtransmission devices 940 and 945. For example, the PDCP transmissiondevice 935 may deliver a packet [1] and a packet [3] to the first RLCtransmission device 940, and a packet [2] and a packet [4] o the secondRLC transmission device 945.

The first RLC transmission device 940 may deliver packets to a first RLCreception device 950, and the second RLC transmission device 945 maydeliver packets to a second RLC reception device 955. The first RLCreception device 950 may reorder the received packets in the order inwhich the first RLC transmission device 940 has received the packetsfrom the PDCP transmission device 935. In other words, the first RLCreception device 950 may deliver packets to a PDCP reception device 960in the order of packet [1] and packet [3]. Similarly, the second RLCreception device 955 may reorder the received packets in the order inwhich the second RLC transmission device 945 has received the packetsfrom the PDCP transmission device 935. In other words, the second RLCtransmission device 945 may deliver packets to the PDCP reception device960 in the order of packet [2] and packet [4].

However, the packets delivered by the first RLC reception device 950 andthe second RLC reception device 955 may not be in sequence. For example,the packets delivered by the first RLC reception device 950 and thesecond RLC reception device 955 may be delivered in the order of packet[1], packet [2], packet [4] and packet [3], or in the order of packet[2], packet [4], packet [1] and packet [3]. Therefore, the PDCPreception device 960 may need to reorder the packets delivered by two ormore RLC reception devices 950 and 955.

In an embodiment of the present disclosure, whether an arbitrary missingPDCP SDU [x] is reordered may be determined depending on whether areordering condition 3 is satisfied. The reordering condition 3 may besummarized as follows.

Reordering Condition 3 of Arbitrary PDCP SDU [x]

PDCP SDUs with COUNT higher than X have been received from both of anMCG RLC and an SCG RLC, and an associated timer 1 has expired.

The timer 1 is started, if a PDCP SDU with COUNT higher than x isreceived from an RLC SCG, and the timer 1 is to cope with anout-of-sequence reception phenomenon between an MeNB and an SeNB.

In the following description, an expression that an arbitrary missingPDCP SDU [x] is reordered may mean performing the subsequent operation,considering that the SDU [x] is received, since there is no possibilityof receiving the missing SDU [x] any longer. If the missing SDU [x] isreordered, SDUs whose COUNT is between [x+1] and y, among the receivedSDUs with COUNT higher than x may be delivered to the upper layer, andthen Last_Submitted_PDCP_RX_COUNT may be updated to y, which is a valueobtained by subtracting 1 from COUNT of the first missing PDCP SDU,which is higher than x. For example, Table 2 below shows reordering anda related operation in a PDCP reception device.

TABLE 2 MCG SCG Last_Submitted_(—) T1 RLC RLC PDCP_RX_COUNT timer PDCPoperation t₀ 10 t₁ 11 11 Deliver [11] to upper layer t₂ 13 11 Store [13]in buffer; [12] is missing SDU t₃ 15 11 Start Store [13] T1 and [15] intimer buffer related to [15] t₄ 14 11 Store [13], [14] and[15] in buffert₅ 15 T1 Consider that [12] timer is no longer re- expire ceived. SDUsbe- tween 12 and 16 are delivered to upper layer, since the firstmissing COUNT higher than 12 is 16.

For example, if SDU[11] is received from the MCG RLC at an arbitrarytime t1, the SDU may be delivered to the upper layer and a relatedvariable may be updated to 11, since the SDU is an in-sequence SDU.

If SDU[13] is received from the MCG RLC at an arbitrary time t2, amissing RLC SDU[12] may occur and the UE may store SDU[13] in the PDCPbuffer.

Thereafter, the UE may receive SDU[15] from the SCG RLC at an arbitrarytime t3. The UE may start a T1 timer, since COUNT of the SDU receivedfrom the SCG RLC is higher than the missing COUNT. If a missing PDU isnot received before the T1 timer expires, it means that the missing PDUis not received from at least the SCG RLC.

Thereafter, the UE may receive SDU[14] from the SCG RLC at an arbitrarytime t4, and thereafter, the T1 timer related to SDU[15] (or related toSDU[12]) may expire at an arbitrary time t5. Since COUNT higher than themissing COUNT has been received from both of the MCG RLC and SCG RLC,and a related T1 timer has expired, the UE may deliver PDCP SDUs [13],[14] and [15] which are SDUs whose COUNT is between COUNT=12 higher by 1than the missing SDU and COUNT=16 of the next missing SDU, to the upperlayer, and update Last_Submitted_PDCP_RX_COUNT to 15.

When it is determined that an arbitrary PDCP SDU is not received asdescribed above, the timer 1 may be related to ‘the lowest COUNTreceived from the SCG RLC among the COUNTs higher than the missingCOUNT’, ‘the COUNT that is first received from the SCG RLC, among theCOUNTs higher than the missing COUNT’, or ‘the missing COUNT’. In theabove example, the timer 1 may be a timer 1 related to 12 or 15, sincethe sequence number of the missing SDU is 12 and COUNT that is firstreceived from SCG RLC, among the COUNTs higher than 12, is 15. The sizeof the timer 1 may be determined as a size that is large enough to copewith the out-of-sequence reception which may occur between the MeNB andSeNB. In other words, the size of the timer 1 may be determined tocorrespond to the possible maximum value in the reception timedifference between two packets which have undergone the out-of-sequencereception phenomenon, which is defined as a phenomenon in which a packetthat the MeNB transmitted to the SeNB at an arbitrary time arrives atthe SeNB earlier than a packet that was transmitted before the packet.

FIG. 10 illustrates an operation of a PDCP reception device in an LTEsystem according to an embodiment of the present disclosure. This is anoperation performed when a PDCP reception device of a multi-bearerreceives a PDCP PDU from an RLC reception device.

Referring to FIG. 10, in operation 1005, the PDCP reception device mayreceive a PDCP PDU [x] from an RLC reception device. In operation 1010,the UE may decipher the PDCP PDU [x] and decompress a header of an IPpacket contained in the PDCP PDU [x] to reconfigure (i.e., convert orrestore) the PDCP PDU [x] into a PDCP SDU [x]. If the PDCP SDU [x] isreceived in duplicate, the UE may discard the PDCP SDU [x] and waituntil the next PDU is received. If the PDCP SDU [x] is not received induplicate, the UE may store the PDCP SDU [x] in a PDCP buffer in theorder of COUNT in operation 1015.

In operation 1020, the UE may determine whether the PDCP SDU [x] hasbeen received from the SCG RLC. If so, to UE may proceed to operation1025, and if not so, the UE may proceed to operation 10445. In operation1025, the UE may determine whether there is a missing SDU with asequence number lower than that of the SDU[x] and the SDU [x] is an SDUthat was first received from the SCG RLC device after the missing SDUoccurred (e.g., whether there is no timer 1 that is in operation inrelation to the missing SDU). If the condition is satisfied, the UE mayproceed to operation 1030, and if the condition is not satisfied, the UEmay proceed to operation 1045. In operation 1030, the UE may start thetimer 1, and associate the timer 1 with COUNT (e.g., received COUNT,missing COUNT, or a value obtained by adding 1 to received COUNT)related to the missing SDU.

In operation 1035, the PDCP reception device may determine whether thereis an in-sequence SDU among the SDUs stored in the PDCP buffer. Forexample, if an SDU[x] was a missing SDU, the above condition may besatisfied, and the PDCP reception device may deliver the in-sequenceSDUs to the upper layer in operation 1040. The in-sequence SDUs mayrefer to SDUs between ‘the highest COUNT delivered to the upper layer’or ‘the in-sequence highest COUNT’ and ‘the lowest COUNT among themissing COUNTs’ before the SDU [x] is received. The PDCP receptiondevice may deliver the in-sequence SDUs to the upper layer in order inoperation 1040. If the above condition is not satisfied, the UE mayproceed to operation 1045.

In operations 1045 and 1050, the UE may determine SDUs that can be nolonger received, among the missing SDUs, and determine whether the upperlayer delivery condition 3 is satisfied, in order to deliver thein-sequence SDUs among the SDUs following the SDUs that can be no longerreceived, to the upper layer. First, the UE may determine whether thereis a missing SDU having COUNT that is lower than the highest COUNTreceived from the SCG RLC and the highest COUNT received from the MCGRLC, among the missing SDUs. For example, in a case where COUNT of themissing SDU is 10, the highest COUNT received from the MCG RLC is A, andthe highest COUNT received from the SCG RLC is B, if A and B are bothhigher than 10, the condition may be satisfied, and if even one of themis lower than 10, the condition may not be satisfied. If the conditionis satisfied, the UE may proceed to operation 1050, and if the conditionis not satisfied, the UE may proceed to operation 1060. Hereinafter, forconvenience of description, the missing COUNT satisfying the conditionwill be referred to as Y.

In operation 1050, the UE may determine whether a timer 1 associatedwith the missing SDU or associated with Y has already expired. If so,the UE may proceed to operation 1055, and if not so, the UE may proceedto operation 1060. In operation 1055, the UE may deliver predeterminedSDUs to the upper layer and then proceed to operation 1060. Thepredetermined SDUs may be SDUs between ‘[Y+1] ’ and ‘the lowest COUNTamong the missing COUNTs higher than Y’. For example, if Y is 10 and themissing COUNTs higher than 10 are 15, 20 and 25, the UE may deliver SDU[11], SDU[12], SDU[13] and SDU[14] to the upper layer, and store theremaining SDUs in the PDCP buffer. It may be considered that SDUs up toat least SDU [14] are in sequence. In operation 1060, the UE may waituntil the next PDU is received or the timer 1 expires.

FIG. 11 illustrates an operation performed when a timer 1 expires in thePDCP reception device as illustrated in FIG. 10 according to anembodiment of the present disclosure.

Referring to FIG. 11, in operation 1105, a timer 1 associated with anarbitrary missing PDCP SDU [z] expires. In this case, the UE mayconsider that there is no possibility that the PDCP SDU [z] is missingdue to the out-of-sequence reception phenomenon between the MeNB and theSeNB. In other words, if COUNT higher than z is received from the MCGRLC, the UE may perform the subsequent operation as if SDU[z] isreceived.

In operation 1110, the UE may determine whether the highest COUNTreceived from the SCG RLC and the highest COUNT received from the MCGRLC are higher than z. Since the timer 1 associated with the missing SDU[z] is started when a PDCP SDU with COUNT higher than z is received fromthe SCG RLC, the UE may simply determine in operation 1110 whether thehighest COUNT received from the MCG RLC is higher than z. If thecondition is satisfied in operation 1110, the UE may deliver, inoperation 1115, SDUs preceding the next missing SDU with COUNT higherthan z among the SDUs with COUNT higher than z, to the upper layer,determining that there is no possibility that the missing SDU [z] isreceived any longer, and may consider that SDUs with up to the highestCOUNT among the SDUs delivered to the upper layer are in sequence. Inoperation 1120, the UE may wait until the next PDU is received, or thetimer 1 associated with another missing SDU expires. If the condition isnot satisfied in operation 1110, then the UE may wait until the next PDUis received in operation 1120.

In the present disclosure, the expression that the PDCP receives a PDCPPDU from the MCG RLC may have the same meaning as receiving a PDCP PDUreconfigured from received data from the MCG serving cell or theMCG-MAC. The expression that the PDCP receives a PDCP PDU from the SCGRLC may have the same meaning as receiving a PDCP PDU reconfigured fromreceived data from the SCG serving cell or SCG-MAC.

As another operation of reordering PDCP PDUs according to an embodimentof the present disclosure, a method may be proposed, which includesperforming timer-based reordering if a bearer is reconfigured from asingle bearer to a multi-bearer, determining the time the reorderingoperation is to be stopped, using a timer if the bearer is reconfiguredfrom a multi-bearer to a single bearer, and using the same timers as thetwo timers for performing the reordering and determining the stop time.The timer may be referred to as a reordering timer.

FIG. 20 illustrates a UE operation during a bearer reconfigurationaccording to an embodiment of the present disclosure. First, the UE mayreceive a control message for the bearer reconfiguration from the ENB,and then perform the bearer reconfiguration based on the controlmessage.

Referring to FIG. 20, in operation 2005, a UE may apply the PDCPoperation 1 for a bearer x which is a single bearer. In operation 2010,the UE may receive a control message for reconfiguring the bearer x intoa multi-bearer. In operation 2015, the UE may create/configure an SCGRLC device to be connected with the multi-bearer depending on theconfiguration information indicated by the control message, and thenconnect the SCG RLC device with a PDCP device. In operation 2020, the UEmay switch an operation of the PDCP device from the PDCP operation 1 toa PDCP operation 4. In other words, the UE may determine whether PDCPPDUs are reordered, beginning at a PDCP PDU that is first received afterthe bearer x was reconfigured into a multi-bearer, and then apply thePDCP operation 4 for determining whether to deliver the PDUs to theupper layer. Thereafter, by applying the PDCP operation 4 for the PDCPPDUs of the reconfigured bearer, the UE may perform an operationconverting the PDCP PDUs into PDCP SDUs and delivering the in-sequencePDCP SDUs to the upper layer. The UE may use a timer 3 in determiningwhether PDCP PDUs are reordered.

Upon receiving a control message for instructing to reconfigure themulti-bearer into a single bearer in operation 2025, the UE may releasethe SCG RLC, switch from the PDCP operation 4 to a PDCP operation 5, andstart a timer 3 in operation 2030. The UE may perform the PDCP operation5 while the timer 3 is in operation, and if the timer 3 expires, the UEmay stop the PDCP operation 5 and switch to the PDCP operation 1 inoperation 2035.

As for the PDCP operation 1, the PDCP operation 4 and the PDCP operation5, it may be understood that multiple detailed operations that should beapplied for the PDCP PDUs delivered from the RLC device are listed in aseries of order. Detailed operations constituting these operations andthe order thereof are listed in Table 3 below. The following detailedoperations may be conducted in the order from top to bottom.

TABLE 3 PDCP operation 1 PDCP operation 4 PDCP operation 5 PDCP PDUreception PDCP PDU reception PDCP PDU reception Determine HFN/ DetermineHFN/ Determine HFN/ COUNT of PDCP COUNT of PDCP COUNT of PDCP PDU.Discard PDU PDU. Discard PDU PDU. Discard PDU if it is received if it isreceived if it is received in duplicate. in duplicate. in duplicate.Process PDCP PDU Process PDCP PDU Process PDCP PDU into PDCP SDU intoPDCP SDU into PDCP SDU Deliver the PDCP Deliver PDCP Store PDCP SDU andPDCP SDU satisfying SDU in the SDUs satisfying upper layer PDCP buffer.upper layer delivery Deliver PDCP delivery condition 4 to SDUssatisfying condition 1 to the upper layer. upper layer delivery theupper layer. Store the re- condition 5 to the Store the re- maining SDUsin upper layer. Store maining SDUs in the PDCP buffer. the remainingSDUs the buffer. in the PDCP buffer.Upper Layer Delivery Condition 5 of PDCP Operation 5

In the PDCP operation 5 that is applied while the timer 3 is inoperation, if a sequence number of a received PDCP SDU is a sequencenumber of a missing PDCP SDU with the lowest sequence number/COUNT(e.g., if Received PDCP SN is the same as a value obtained by adding 1to Last_Submitted_PDCP_RX_SN), the UE may deliver, to the upper layer,SDUs with consecutive sequence numbers/COUNTs up to the next missingPDCP SDU, including the received PDCP SDU. If the received PDCP SDU isnot a missing PDCP SDU with the lowest sequence number, the PDCP SDU maybe stored in the PDCP buffer. If the timer 3 expires, the UE may deliverall the PDCP SDUs that are currently stored in the PDCP buffer, to theupper layer in the order of COUNT, and store the sequence number of thelast delivered PDCP SDU in Last_Submitted_PDCP_RX_SN.

Hereinafter, for convenience of description, the sequence number will beinterchangeably used with COUNT.

Upper Layer Delivery Condition 4 of PDCP Operation 4

If a sequence number of a received PDCP SDU is a sequence number of amissing PDCP SDU with the lowest sequence number (e.g., if Received PDCPSN is the same as a value obtained by adding 1 toLast_Submitted_PDCP_RX_SN), the UE may deliver, to the upper layer, thesequentially received SDUs up to the next missing PDCP SDU, includingthe received PDCP SDU. If the received PDCP SDU is not a missing PDCPSDU with the lowest sequence number, the PDCP SDU may be stored in thePDCP buffer. If the timer 3 is in operation, the UE may wait until thenext PDCP PDU is received, and if the timer 3 is not in operation, theUE may start the timer 3 and store, in Reordering_PDCP_RX_COUNT, COUNTshigher by 1 than the highest COUNT among the COUNTs of the PDCP SDUsthat were received at the time. If the timer 3 expires, the UE maydeliver PDCP SDUs with COUNT lower than Reordering_PDCP_RX_COUNT andPDCP SDUs associated with consecutive COUNTs higher thanReordering_PDCP_RX_COUNT, to the upper layer. For example, in a casewhere a PDCP SDU with Reordering_PDCP_RX_COUNT=N and COUNT=N+M is notreceived, and PDCP SDUs between N and [N+M] are all stored in the PDCPbuffer, if the timer 3 expires, the UE may all the PDCP SDUs with COUNTlower than N and all the PDCP SDUs with COUNT between N and [N+M−1]including them, among the SDUs stored in the PDCP buffer, to the upperlayer. In addition, the UE may store a sequence number of the lastdelivered PDCP SDU in Last_Submitted_PDCP_RX_SN.

FIG. 21 illustrates an operation of a PDCP reception device operatingwith a multi-bearer according to an embodiment of the presentdisclosure. This shows an operation of a PDCP reception operation thathas received a packet from an RLC reception device.

Referring to FIG. 21, in operation 2105, the PDCP reception device mayreceive a PDCP PDU [x] from the RLC reception device. In operation 2110,the PDCP reception device may determine HFN of the received packet,using the received packet's sequence number (Received PDCP SN),Next_PDCP_RX_SN, Reordering_Window, and Last_Submitted_PDCP_RX_SN. ThePDCP reception device may calculate COUNT associated with the PDCPpacket by concatenating the determined HFN and the Received PDCP SN. Inaddition, the UE may decipher the PDCP PDU [x] by applying the COUNT,and decompress a header of an IP packet contained in the PDCP PDU [x] toreconfigure (i.e., convert or restore) the PDCP PDU [x] into a PDCP SDU[x]. If the PDCP SDU [x] is received in duplicate, the UE may discardthe PDCP SDU [x] and wait until the next PDU is received. If the PDCPSDU [x] is not received in duplicate, the UE may store the PDCP SDU [x]in the PDCP buffer in the order of COUNT in operation 2115.

In operation 2120, the PDCP reception device may determine whether thereceived packet is a missing packet with the lowest COUNT. If thefollowing condition is satisfied, meaning that the received packet is amissing packet with the lowest COUNT, the UE may proceed to operation2130, and if the following condition is not satisfied, the UE may waituntil the next PDCP PDU is received, in operation 2125.

Condition for Determining Whether Received Packet is Missing Packet withLowest COUNTReceived PDCP SN=Last_Submitted_PDCP_RX_SN+1; orreceived PDCP SN=Last_Submitted_PDCP_RX_SN−Maximum_PDCP_SN

In operation 2130, the PDCP reception device may deliver the PDCP SDUsassociated with the consecutive COUNTs among the PDCP SDUs stored in thePDCP buffer to the upper layer in the order of COUNT, beginning at theCOUNT of the received PDCP SDU, and set Last_Submitted_PDCP_RX_SN to asequence number of the last delivered PDCP SDU. For example, if PDCPSDUs with COUNTs=[M], [M+1], [M+2], [M+4] and [M+5] are stored in thePDCP buffer and a PDCP SDU with COUNT=[M−1] is received, the PDCPreception device may deliver the PDCP SDUs with COUNTs=[M−1], [M], [M+1]and [M+2] to the upper layer.

In operation 2135, the PDCP reception device may determine whether atleast one PDCP SDU is still stored in the PDCP buffer without being insequence, after the PDCP reception device performed the above operation.If so, the PDCP reception device may proceed to operation 2140, and ifnot so, the PDCP reception device may proceed to operation 2125.

In operation 2140, the PDCP reception device may determine whether thetimer 3 is in operation. If so, the PDCP reception device may proceed tooperation 2125, and if the timer 3 is not in operation, the PDCPreception device may proceed to operation 2145.

In operation 2145, the PDCP reception device may start the timer 3, andset Reordering_PDCP_RX_COUNT to a value obtained by concatenating RX_HFNand Next_PDCP_RX_SN. In other others, the PDCP reception device maystore, in Reordering_PDCP_RX_COUNT, a value higher by 1 than the highestCOUNT that has been received so far. Thereafter, the PDCP receptiondevice may proceed to operation 2125.

FIG. 22 illustrates an operation of a PDCP reception device thatswitches to a PDCP operation 5 when reconfiguring a bearer from amulti-bearer into an MCG bearer according to an embodiment of thepresent disclosure.

An MCG bearer may be a bearer in which data is transmitted and receivedonly through the MCG, among the single bearers. If the PDCP receptiondevice releases the SeNB and the SCG while performing DC for reasonsthat the UE is out of the area of the SeNB, the multi-bearer may bereconfigured into an MCG bearer.

Referring to FIG. 22, in operation 2205, the PDCP reception device mayreceive a control message for instructing to reconfigure a multi-bearerinto an MCG bearer. The control message may be, for example, aninstruction to reconfigure a multi-bearer into an MCG bearer explicitly,and the control message may be a control message for releasing the lastSCG cell, though the control message is not an explicit reconfigurationinstruction.

In operation 2210, the PDCP reception device may release the SCG-RLC ofa multi-bearer, assemble in PDCP PDUs all the PDCP SDUs that can beassembled in PDCP PDUs, among the RLC packets stored in the RLC, andthen deliver the assembled PDCP PDUs to the upper layer.

In operation 2215, the PDCP reception device may determine whether thetimer 3 is currently in operation. Operation 2215 may be performed, forexample, as soon as the analysis of a control message for instructingswitching to the MCG bearer is completed, or may be performed when aPDCP PDU is received from the released SCG-RLC.

If the timer 3 is not in operation, the PDCP reception device mayproceed to operation 2225, and if the timer 3 is in operation, the PDCPreception device may proceed to operation 2220. In operation 2220,several operations are possible. The PDCP reception device may performone of the following operations 1) to 3).

1) The PDCP reception device may stop the timer 3 that is currently inoperation, restart the timer 3, and then proceed to operation 2230.

2) The PDCP reception device may restart the timer 3 after waiting forthe expiry of the timer 3 that is currently in operation, and thenproceed to operation 2230.

3) Upon receiving a PDCP PDU from the released SCG-RLC, the PDCPreception device may stop the timer 3 that is currently in operation,restart the timer 3, and then proceed to operation 2230. If no PDCP PDUis received from the released SCG-RLC, the PDCP reception device maykeep the timer 3 that is currently in operation, and switch to the PDCPoperation 1 at the time the timer 3 that is currently in operationexpires, without proceeding to operation 2230.

In operation 2225, several operations are possible. The PDCP receptiondevice may perform one of the following operations a) and b).

a) The PDCP reception device may start the timer 3, and proceed tooperation 2230.

b) Upon receiving a PDCP PDU from the released SCG-RLC, the PDCPreception device may start the timer 3, and proceed to operation 2230.If no PDCP PDU is received from the released SCG-RLC, the PDCP receptiondevice may immediately switch to the PDCP operation 1 without proceedingto operation 2230.

In operation 2230, the PDCP reception device may wait until the timer 3expires, and if the timer 3 expires, the PDCP reception device maydeliver all the PDCP SDUs which are currently stored in the PDCP buffer,to the upper layer in the order of COUNT, and setLast_Submitted_PDCP_RX_SN to a sequence number of the last deliveredSDU. Thereafter, the PDCP reception device may switch to the PDCPoperation 1.

FIG. 23 illustrates an operation of a PDCP reception device performedwhen a timer 3 expires according to an embodiment of the presentdisclosure.

Referring to FIG. 23, in operation 2305, a timer 3 of the PDCP receptiondevice of an arbitrary bearer may expire.

In operation 2310, the PDCP reception device may determine whether thebearer is a multi-bearer or an MCG bearer. If the bearer is amulti-bearer, the PDCP reception device may proceed to operation 2315,and if bearer is an MCG bearer, the PDCP reception device may proceed tooperation 2320. Proceeding to operation 2320 means that the bearer isreconfigured from a multi-bearer into an MCG bearer, and since the timer3 has expired, the PDCP reception device may stop the PDCP operation 5,and deliver all the PDCP SDUs currently stored in the PDCP buffer to theupper layer to switch to the PDCP operation 1.

Proceeding to operation 2315 means that the PDCP reception deviceoperates in the PDCP operation 4, and the PDCP reception device maydeliver all the PDCP SDUs with COUNTs lower thanReordering_PDCP_RX_COUNT and all the PDCP SDUs associated withconsecutive COUNTs among the PDCP SDUs stored in the PDCP buffer to theupper layer beginning at the Reordering_PDCP_RX_COUNT based on theReordering_PDCP_RX_COUNT. In other words, the PDCP reception device maydeliver PDCP SDUs corresponding to the condition in Table 4 below to theupper layer.

TABLE 4 all stored PDCP SDU(s) with an associated COUNT value less thanReordering_PDCP_RX_COUNT; all stored PDCP SDU(s) with consecutivelyassociated COUNT value(s) starting from Reordering_PDCP_RX_COUNT;

The PDCP reception device may update the Last_Submitted_PDCP_RX_SN inoperation 2325, and determine in operation 2330 whether at least one ofthe PDCP SDUs is left in the PDCP buffer. If at least one PDCP SDU isleft in the PDCP buffer, the PDCP reception device may proceed tooperation 2335, and if no PDCP SDU is left in the PDCP buffer, the PDCPreception device may proceed to operation 2340.

In operation 2335, the PDCP reception device may start the timer 3 andset Reordering_PDCP_RX_COUNT to a value obtained by concatenating RX_HFNand Next_PDCP_RX_SN.

In operation 2340, the PDCP reception device may wait until the nextPDCP PDU arrives.

As shown in the above example, in determining whether a received PDCPSDU is a missing SDU, the PDCP reception device may use a variable thatis managed by the sequence number of the PDCP SDU, and in determining aPDCP SDU that is to be delivered to the upper layer as the timer 3expires, the PDCP reception device may use a variable that is managed bythe COUNT.

As another operation of reordering PDCP PDUs according to an embodimentof the present disclosure, a method may be proposed, which includesperforming timer-based reordering if a bearer is reconfigured from asingle bearer to a multi-bearer, determining the time the reorderingoperation is to be stopped, using a timer if the bearer is reconfiguredfrom a multi-bearer to a single bearer, and determining the amount ofdata stored in a reordering buffer and whether the lower layer isreestablished, in order to determine the stop time.

FIG. 24 illustrates a UE operation during a bearer reconfigurationaccording to an embodiment of the present disclosure.

Referring to FIG. 24, in operation 2405, the UE may apply a PDCPoperation 6 for a bearer x which is a single bearer. In operation 2410,the UE may receive a control message for reconfiguring the bearer x intoa multi-bearer. In operation 2415, the UE may generate/configure an SCGRLC device to be connected with the multi-bearer depending on theconfiguration information indicated by the control message, and thenconnect the SCG RLC device with the PDCP device. In operation 2420, theUE may switch the operation of the PDCP device from the PDCP operation 6to a PDCP operation 7. The PDCP operation 6 will be described later. Inother words, the UE may apply the PDCP operation 7 for PDCP PDUs inorder beginning at the PDCP PDU that is first received after the beareris reconfigured into a multi-bearer, and the PDCP operation 7 will bedescribed later. Thereafter, by applying the PDCP operation 7 for thePDCP PDUs of the bearer that is reconfigured into the multi-bearer, theUE may determine whether the received PDCP PDUs are reordered, convertthe in-sequence PDCP PDUs into PDCP SDUs, and deliver the PDCP SDUs tothe upper layer. In determining whether the PDCP PDUs are in sequence,the UE may use a timer 3.

Upon receiving a control message for instructing to reconfigure themulti-bearer into a single bearer in operation 2425, the UE may releasethe SCG RLC in operation 2430. Because of the release of the SCG RLC,out-of-sequence PDCP PDUs may be delivered to the PDCP device, and thePDCP device may continue to apply the PDCP operation 7 for the PDCPPDUs. The PDCP operation 7 may be applied until a reordering stopcondition is satisfied, and if the reordering stop condition issatisfied, the UE may determine in operation 2435 whether the reorderingstop condition is satisfied due to ‘reestablishment of lower layer’ or‘absence of out-of-sequence packet’. If the reordering stop condition issatisfied due to ‘absence of out-of-sequence packet’, the UE may switchto the PDCP operation 6 in operation 2440, and then end the process. Onthe other hand, if the reordering stop condition is satisfied due to‘reestablishment of lower layer’, the UE may proceed to operation 2445.The lower layer may be an MCG-RLC device. In this case, since the UE hasalready switched to the single bearer, the PDCP device may be connectedonly with one RLC device, and the only RLC device may be reestablished.In operation 2445, the UE may order the PDCP PDUs currently stored in areordering buffer and the PDCP PDUs delivered due to the reestablishmentof the lower layer, in the order of COUNT, process the PDCP PDUs intoPDCP SDUs in the order of COUNT, switch to the PDCP operation 6, andthen end the process. In this case, the PDCP device may process the PDCPPDUs stored in the reordering buffer as if they are PDCP PDUs delivereddue to the reestablishment of the lower layer.

As for the PDCP operation 6 and the PDCP operation 7, it may beunderstood that multiple detailed operations that should be applied forthe PDCP PDUs delivered from the RLC device are listed in a series oforder. Detailed operations constituting these operations and the orderthereof are listed in Table 5 below. The following detailed operationsmay be conducted in the order from top to bottom.

TABLE 5 PDCP operation 6 PDCP operation 7 PDCP PDU reception PDCP PDUreception Determine HFN/COUNT Determine HFN/ of PDCP PDU. Process COUNTof PDCP PDU. PDU received in duplicate into PDCP SDU, and then discardPDU received in duplicate Process PDCP Process PDCP PDU satisfying PDUinto PDCP SDU upper layer delivery condition 7 into PDCP SDU, deliverPDCP SDU to the upper layer, and store the remaining PDUs in PDCP bufferDeliver the PDCP SDU and PDCP SDUs satisfying upper layer deliverycondition 1 to the upper layer. Store the remaining SDUs in the buffer.

While the UE determines in the PDCP operation 6 whether duplicatereception happens, the UE may not determine in the PDCP operation 7whether duplicate reception happens. This is because in a case where thePDCP operation 6 is applied, the packet that has already been receivedafter a handover is likely to be received in duplicate, but there is nosuch possibility in the PDCP operation 7. A PDU received in duplicatemay be processed into an SDU before being discarded, in order to updatea header decompression context. In a situation where the PDCP operation7 is applied, it is not necessary for the UE to perform an operation ofdetermining a packet received in duplicate, processing the packetreceived in duplicate into an SDU, and then discarding the packetreceived in duplicate.

In the PDCP operation 6, the UE may first process received PDUs intoSDUs, and then store out-of-sequence SDUs in a buffer and deliverin-sequence SDUs to the upper layer. On the other hand, in the PDCPoperation 7, the UE may first determine whether received PDUs are insequence, and only for the in-sequence PDUs, the UE may process the PDUsinto SDUs and deliver the SDUs to the upper layer. The UE may store theout-of-sequence PDUs in the buffer without processing them into SDUs.The reason is as follows.

In a case where the PDCP operation 6 is applied, if a packet [X] isreceived, the UE may not determine whether the received packet [X] isreordered, since a packet with a sequence number lower than that of thepacket [X] is no longer received, so there is no problem with a headerdecompression operation even though the UE processes the received packetinto SDUs. However, in a case where the PDCP operation 7 is applied,since out-of-sequence packets may be received at all times, the UEshould process the received packets into SDUs after first reordering thereceived packets, in order to prevent errors in the header decompressionoperation.

An upper layer delivery condition 7 of the PDCP operation 7 may be forPDCP PDUs instead of PDCP SDUs, and the upper layer delivery condition 7may be the same as the upper layer delivery condition 4 except that thepacket satisfying the condition is delivered not to the upper layer, butto the PDCP PDU processing device.

Upper Layer Delivery Condition 7 of PDCP Operation 7

If a sequence number of a received PDCP PDU is a sequence number of amissing PDCP PDU with the lowest sequence number (e.g., if Received PDCPSN is the same as a value obtained by adding 1 toLast_Submitted_PDCP_RX_SN), the UE may deliver the sequentially receivedPDUs up to the next missing PDCP PDU, including the received PDCP PDU,to a processing device (e.g., a header decompression device or adeciphering device). The deciphering device may refer to a device fordeciphering received PDCP PDUs. The PDUs may be delivered to the upperlayer after being processed into SDUs in the processing device. If thereceived PDCP PDU is not a missing PDCP PDU with the lowest sequencenumber, the PDCP PDU may be stored in the PDCP buffer. If the timer 3 isin operation, the UE may wait until the next PDCP PDU is received, andif the timer 3 is not in operation, the UE may start the timer 3, andstore, in Reordering_PDCP_RX_COUNT, COUNTs higher by 1 than the highestCOUNT among the COUNTs of the PDCP PDUs that were received at the time.If the timer 3 expires, the UE may deliver the PDCP PDUs with COUNTlower than Reordering_PDCP_RX_COUNT and the PDCP PDUs associated withconsecutive COUNTs higher than Reordering_PDCP_RX_COUNT, to theprocessing device. The UE may store a sequence number of the lastdelivered PDCP SDU in Last_Submitted_PDCP_RX_SN.

If the multi-bearer is reconfigured into a single bearer, the UE shouldswitch the PDCP operation from the PDCP operation 7 to the PDCPoperation 6. In an embodiment of the present disclosure, the PDCP devicemay continue to apply the PDCP operation 7 until the reordering stopcondition is satisfied after the multi-bearer is reconfigured into asingle bearer, and if the reordering stop condition is satisfied, thePDCP device may switch to the PDCP operation 6. The reordering stopcondition may be satisfied, if a lower layer is reestablished(reestablishment of lower layer) or there is no more PDU to be reordered(absence of out-of-sequence packet).

The establishment of a lower layer may occur if a UE that was operatingwith, for example, a single bearer receives a handover instruction. Inthis case, the out-of-sequence PDCP PDUs stored in the MCG-RLC deviceare all delivered to the PDCP reception device, and the UE may switch tothe PDCP operation 6 of processing the out-of-sequence PDCP PDUscurrently stored in the PDCP buffer and the PDCP PDUs delivered from thelower layer, into PDCP SDUs in sequence in the order of COUNT,delivering the in-sequence SDUs to the upper layer, storing theout-of-sequence SDUs in the buffer, and then determining the SDUs to bedelivered to the upper layer, based on the sequence numbers of the PDUsreceived from the newly established lower layer.

The expression that there is no more PDU to be reordered may refer to acase where as a result of the reordering operation using the timer 3,there is no more missing PDU after the UE processes the PDUs, which wereregarded to be out of sequence by the missing PDUs as the timer 3associated with the missing PDUs expires, into SDUs, and then deliversthe SDUs to the upper layer. For example, if a value obtained by adding1 to Last_Submitted_PDCP_RX_SN is the same as Next_PDCP_RX_SN, it maymean that there is no more missing PDU, or there is no moreout-of-sequence PDU. Since the expression that the condition issatisfied means that there is no more PDU stored in the PDCP buffer, thePDCP reception device may immediately switch to the PDCP operation 6.

The PDCP operation 7 is the same as the PDCP operation 4 shown in FIG.25 except for the following, so a detailed description thereof will beomitted.

FIG. 25 illustrates a PDCP operation 7 of a PDCP reception deviceoperating with a multi-bearer according to an embodiment of the presentdisclosure. An example of FIG. 25 shows an operation of a PDCP receptiondevice that has received a packet from an RLC reception device.

Referring to FIG. 25, in operation 2505, the PDCP reception device mayreceive a PDCP PDU [x] from the RLC reception device. In operation 2510,the PDCP reception device may determine HFN of the received packet,using the received packet's sequence number (Received PDCP SN),Next_PDCP_RX_SN, Reordering_Window, and Last_Submitted_PDCP_RX_SN. ThePDCP reception device may calculate COUNT associated with the PDCPpacket by concatenating the determined HFN and the Received PDCP SN. Byapplying the COUNT, the PDCP reception device may determine whether thereceived packet is a missing packet with the lowest COUNT.

If the following condition is satisfied in operation 2520, meaning thatthe received packet is a missing packet with the lowest COUNT, the PDCPreception device may proceed to operation 2530, and if the followingcondition is not satisfied, the PDCP reception device may wait inoperation 2525 until the next PDCP PDU is received.

Condition for Determining Whether Received Packet is Missing Packet withLowest COUNTReceived PDCP SN=Last_Submitted_PDCP_RX_SN+1; orreceived PDCP SN=Last_Submitted_PDCP_RX_SN−Maximum_PDCP_SN

In operation 2530, the PDCP reception device may process PDCP PDUsassociated with consecutive COUNTs among the PDCP PDUs stored in thePDCP buffer into PDCP SDUs in the order of COUNT, beginning at the COUNTof the received PDCP PDU, and then deliver the PDCP SDUs to the upperlayer, and may set Last_Submitted_PDCP_RX_SN to a sequence number of thelast delivered PDCP SDU. For example, if PDCP PDUs with COUNTs=[M],[M+1], [M+2], [M+4] and [M+5] are stored in the PDCP buffer and a PDCPPDU with COUNT=[M−1] is received, the PDCP reception device may deliverPDCP PDUs with COUNTs=[M−1], [M], [M+1] and [M+2] to the next processingdevice to convert them into PDCP SDUs, and then deliver the PDCP SDUs tothe upper layer. In operation 2535, the PDCP reception device maydetermine whether at least one PDCP PDU is still stored in the PDCPbuffer without being in sequence, after the PDCP reception deviceperformed the above operation. If so, the PDCP reception device mayproceed to operation 2540, and if not so, the PDCP reception device mayproceed to operation 2525.

In operation 2540, the PDCP reception device may determine whether atimer 3 is in operation. If so, the PDCP reception device may proceed tooperation 2525, and if not so, the PDCP reception device may proceed tooperation 2545. In operation 2545, the PDCP reception device may startthe timer 3, and set Reordering_PDCP_RX_COUNT to a value obtained byconcatenating RX_HFN and Next_PDCP_RX_SN. In other words, the PDCPreception device may store, in Reordering_PDCP_RX_COUNT, a value higherby 1 than the highest COUNT that has been received so far. Thereafter,the PDCP reception device may proceed to operation 2525.

FIG. 26 illustrates an operation of a PDCP reception device performedwhen a timer 3 expires according to an embodiment of the presentdisclosure.

Referring to FIG. 26, in operation 2605, a timer 3 of a PDCP receptiondevice of an arbitrary bearer expires. In operation 2615, the PDCPreception device may deliver all the PDCP PDUs with COUNTs lower thanReordering_PDCP_RX_COUNT and the PDCP PDUs associated with consecutiveCOUNTs among the PDCP PDUs stored in the PDCP buffer into PDCP SDUs inthe order of COUNT, beginning at the Reordering_PDCP_RX_COUNT based onthe Reordering_PDCP_RX_COUNT, and then deliver the PDCP SDUs to theupper layer. In other words, the PDCP reception device may process PDCPPDUs corresponding to the condition in Table 6 below into PDCP SDUs, andthen deliver the PDCP SDUs to the upper layer.

TABLE 6 all stored PDCP PDU(s) with an associated COUNT value less thanReordering_PDCP_RX_COUNT; all stored PDCP PDU(s) with consecutivelyassociated COUNT value(s) starting from Reordering_PDCP_RX_COUNT;

The PDCP reception device may update Last_Submitted_PDCP_RX_SN inoperation 2625, and determine in operation in operation 2630 whether atleast one PDCP PDU is left in the PDCP buffer. If at least one PDCP PDUis left in the PDCP buffer, the PDCP reception device may proceed tooperation 2635, and if at least one PDCP PDU is not left in the PDCPbuffer, the PDCP reception device may proceed to operation 2640. Inoperation 2635, the PDCP reception device may start a timer 3, and setReordering_PDCP_RX_COUNT to a value obtained by concatenating RX_HFN andNext_PDCP_RX_SN. In operation 2640, the PDCP reception device may waituntil the next PDCP PDU arrives.

As another operation of reordering PDCP PDUs according to an embodimentof the present disclosure, a method may be proposed, in which a bearermay be reconfigured from a single bearer to a multi-bearer, and the PDCPreception device may operate with the multi-bearer. In this embodiment,if a bearer is reconfigured from a single bearer to a multi-bearer, theUE may process in-sequence PDUs among the received PDCP PDUs into PDCPSDUs, and then deliver the PDCP SDUs to the upper layer, and may processout-of-sequence PDCP PDUs into half PDCP SDUs, and then store the halfPDCP SDUs in the buffer until they are in sequence. Thereafter, if thePDCP PDUs stored in the buffer are in sequence, the UE may convert thehalf PDCP SDUs into PDCP SDUs and deliver the PDCP SDUs to the upperlayer. The PDCP processing operation may include deciphering and headerdecompression, and the received PDCP PDUs may be converted into PDCPSDUs after going through the entire operation (deciphering and headerdecompression). Here, the term ‘half PDCP SDU’ may refer to a packetobtained by applying only some of the PDCP processing operation to thePDCP PDU (e.g., a packet to which deciphering is applied, but headerdecompression is not applied).

The reason for deciphering a packet received on the multi-bearer, andthen storing the deciphered packet in the reordering buffer is that ifan SCG of the UE is changed, a deciphering key may be changed, and inthis case, if a PDCP PDU that has not been deciphered yet is stored inthe PDCP device to be reordered, the UE should apply different securitykeys to the previous PDCP PDU and the newly received PDCP PDU, resultingin an increase in complexity.

FIG. 28 illustrates a UE operation during a bearer reconfigurationaccording to an embodiment of the present disclosure.

Referring to FIG. 28, in operation 2805, the UE may apply the PDCPoperation 6 for a bearer x which is a single bearer. In operation 2810,the UE may receive a control message for reconfiguring the bearer x intoa multi-bearer. In operation 2815, the UE may generate/configure an SCGRLC device to be connected with the multi-bearer depending on theconfiguration information indicated by the control message, and thenconnect the SCG RLC device with the PDCP device. In operation 2820, theUE may switch an operation of the PDCP device from the PDCP operation 6to a PDCP operation 8. In other words, the UE may apply the PDCPoperation 8 for PDCP PDUs in sequence, beginning at the PDCP PDU that isfirst received after the bearer is reconfigured into the multi-bearer.

Specifically, by applying the PDCP operation 8 for the PDCP PDUs of thebearer that is reconfigured into the multi-bearer, the UE may processin-sequence PDCP PDUs among the received PDCP PDUs into PDCP SDUs, anddeliver the PDCP SDUs to the upper layer, and may processout-of-sequence PDCP PDUs into half PDCP SDUs, store the half PDCP SDUsin the PDCP reordering buffer, and then start a timer 3 if necessary.

Thereafter, upon receiving a control message for instructing toreconfigure the multi-bearer into a single bearer in operation 2825, theUE may release the SCG RLC in operation 2830. Because of the release ofthe SCG RLC, out-of-sequence PDCP PDUs may be delivered to the PDCPdevice, and the PDCP device may continue to apply the PDCP operation 8for the PDCP PDUs. The PDCP operation 8 may be applied until areordering stop condition is satisfied, and if the reordering stopcondition is satisfied, the UE may determine in operation 2835 whetherthe reordering stop condition is satisfied due to ‘reestablishment oflower layer’ or ‘absence of out-of-sequence packet’. If it is determinedin operation 2835 that the reordering stop condition is satisfied due to‘absence of out-of-sequence packet’, the UE may switch to the PDCPoperation 6 in operation 2840, and then end the process. On the otherhand, if it is determined in operation 2835 that the reordering stopcondition is satisfied due to ‘reestablishment of lower layer’, the UEmay proceed to operation 2845. Here, the lower layer may be, forexample, an MCG-RLC device. Since the UE has already switched to thesingle bearer, the PDCP device may be connected only with one RLCdevice, and the only RLC device may be the lower layer. In operation2845, the UE may determine whether there is in-sequence PDCP PDU or halfPDCP SDU, referring to the sequence numbers or COUNTs of the PDCP PDUsdelivered due to the reestablishment of the lower layer and the halfPDCP SDUs stored in the reordering buffer, and if there is in-sequencePDCP PDU or half PDCP SDU, the UE may convert the in-sequence PDCP PDUor half PDCP SDU into a PDCP SDU by applying the necessary PDCPprocessing operation, and then deliver the PDCP SDU to the upper layerin the order of COUNT. The UE may convert out-of-sequence half PDCP SDUsand PDCP PDUs into PDCP SDUs, and then store the PDCP SDUs in the PDCPreordering buffer in the order of COUNT. In this case, theout-of-sequence PDCP SDUs may be stored in the PDCP reordering buffer inwhich the half PDCP SDUs were stored. In some cases, the half PDCP SDUsand PDCP SDUs may be stored in the same storage space. In this case, thehalf PDCP SDUs and PDCP SDUs may be stored altogether in the order ofCOUNT, rather than they are stored separately (e.g., the half PDCP SDUsmay be stored among themselves and the PDCP SDUs may be stored amongthemselves). In addition, the UE may switch to the PDCP operation 6.

The fact that it is determined in operation 2845 that there isin-sequence PDCP PDU or half PDCP SDU may refer to the fact that thereis PDCP PDU or half PDCP SDU with a sequence number higher by 1 thanLast_Submitted_PDCP_RX_SN among the PDCP PDUs or half PDCP SDUs.

As for the PDCP operation 6 and the PDCP operation 8, it may beunderstood that multiple detailed operations that should be applied forthe PDCP PDUs delivered from the RLC device are listed in a series oforder. Detailed operations constituting the PDCP operations 6 and 8 andthe order thereof are listed in Table 7 below. In Table 7, detailedoperations may be conducted in the order from top to bottom.

TABLE 7 PDCP operation 6 PDCP operation 8 PDCP PDU reception PDCP PDUreception Determine HFN/COUNT Determine HFN/ of PDCP PDU. Process aCOUNT of PDCP PDU. PDU received in duplicate into Discard a PDU receivedPDCP SDU, and then discard in duplicate without PDU received induplicate processing it into PDCP SDU. Process PDCP Process PDCP PDUinto PDCP SDU PDU into half PDCP SDU Deliver the PDCP SDU Process halfPDCP SDU and PDCP SDUs satisfying satisfying upper layer delivery upperlayer delivery condition 8 into PDCP SDU, condition 1 to the upperdeliver PDCP SDU to the upper layer. Store the remaining layer, andstore the remaining SDUs in the buffer. half PDCP SDUs in the PDCPbuffer.

In the PDCP operation 6, the UE may first process received PDUs intoSDUs, and then store out-of-sequence SDUs in a buffer and deliverin-sequence SDUs to the upper layer. On the other hand, in the PDCPoperation 8, the UE may convert received PDUs into half PDCP SDUs byapplying only a predetermined PDCP processing operation (e.g.,deciphering) to the received PDUs, and then determines whether the PDUsare in sequence. In addition, the UE may process only the in-sequencehalf PDCP SDUs into PDCP SDUs by applying the remaining PDCP processingoperation (e.g., header decompression) for the in-sequence half PDCPSDUs, and then deliver the PDCP SDUs to the upper layer, and may storethe out-of-sequence half PDCP SDUs in the buffer without converting theminto PDCP SDUs.

The following upper layer delivery condition 8 of the PDCP operation 8may be for half PDCP SDUs instead of PDCP SDUs, and the upper layerdelivery condition 8 may be the same as the upper layer deliverycondition 7 except that the packet satisfying the condition is deliverednot to a first PDCP processing device (e.g., a deciphering device), butto a second PDCP processing device (e.g., a header decompressiondevice). In some cases, not only the out-of-sequence half PDCP SDUs butalso the out-of-sequence PDCP SDUs may be stored in the PDCP receptiondevice. In this case, in applying the upper layer delivery condition 8,the PDCP reception device may consider not only the half PDCP SDUs butalso the PDCP SDUs.

Upper Layer Delivery Condition 8 of PDCP Operation 8

If a sequence number of a received PDCP PDU is a sequence number of amissing PDCP with the lowest sequence number (e.g., if Received PDCP SNis the same as a value obtained by adding 1 toLast_Submitted_PDCP_RX_SN), the UE may deliver consecutive half PDCPSDUs up to the next missing PDCP PDU (or half PDCP SDUs correspondingthereto), including the received PDCP PDU (or a half PDCP SDUcorresponding thereto) to the next PDCP processing device (e.g., aheader decompression device). The half PDCP SDUs may be processed intoPDCP SDUs in the next PDCP processing device, and then delivered to theupper layer. If the received PDCP PDU is not a missing PDCP PDU with thelowest sequence number, the PDCP PDU may be processed into a half PDCPSDU, and then stored in the PDCP buffer. If the timer 3 is in operation,the UE may wait until the next PDCP PDU is received, and if the timer 3is not in operation, the UE may start the timer 3, and store,Reordering_PDCP_RX_COUNT, COUNTs higher by 1 than the highest COUNTamong the COUNTs of the PDCP PDUs that were received at the time. If thetimer 3 expires, the UE may deliver half PDCP SDUs with COUNTs lowerthan Reordering_PDCP_RX_COUNT and half PDCP SDUs associated withconsecutive COUNTs higher than Reordering_PDCP_RX_COUNT, to the nextPDCP processing device (e.g., a header decompression device). The UE maydeliver the PDCP SDUs processed in the header decompression device tothe upper layer, and store a sequence number of the last delivered PDCPSDU in Last_Submitted_PDCP_RX_SN.

If the multi-bearer is reconfigured into a single bearer, the UE shouldswitch the PDCP operation from the PDCP operation 8 to the PDCPoperation 6. In an embodiment of the present disclosure, the PDCPprocessing device may continue to apply the PDCP operation 8 until thereordering stop operation is satisfied after the multi-bearer isreconfigured into a single bearer, and if the reordering stop operationis satisfied, the PDCP processing device may switch to the PDCPoperation 6. The reordering stop condition may be satisfied, if a lowerlayer is reestablished (reestablishment of lower layer) or there is nomore PDU to be reordered (absence of out-of-sequence packet).

The establishment of a lower layer may occur if a UE that was operatingwith, for example, a single bearer receives a handover instruction. Inthis case, the out-of-sequence PDCP PDUs stored in the MCG-RLC deviceare all delivered to the PDCP reception device, and the UE may switch tothe PDCP operation 6 of processing the out-of-sequence half PDCP SDUscurrently stored in the PDCP buffer and the PDCP PDUs delivered from thelower layer, into PDCP SDUs in sequence in the order of COUNT,delivering the in-sequence SDUs to the upper layer, storing theout-of-sequence SDUs in the buffer, and then determining the SDUs to bedelivered to the upper layer, based on the sequence numbers of the PDUsreceived from the newly established lower layer.

The expression that there is no more PDU to be reordered may refer to acase where as a result of the reordering operation using the timer 3,there is no more missing PDU after the UE processes the half PDCP SDUs,which were regarded to be out of sequence by the missing PDUs as thetimer 3 associated with the missing PDUs expires, into SDUs, and thendelivers the SDUs to the upper layer. Otherwise, the expression thatthere is no more PDU to be reordered may refer to a case where a PDCPPDU delivered from the lower layer is a missing PDCP PDU with the lowestsequence number. For example, after the bearer is reconfigured from amulti-bearer to a single bearer, if a sequence number of the receivedPDCP PDU is the same as a value obtained by adding 1 toLast_Submitted_PDCP_RX_SN and Last_Submitted_PDCP_RX_SN is the same asNext_PDCP_RX_SN, it may mean that there is no more missing PDU, or thereis no more out-of-sequence half PDCP SDU. Since the expression that thecondition is satisfied means that there is no more half PDCP SDU storedin the PDCP buffer, the PDCP reception device may immediately switch tothe PDCP operation 6.

In an embodiment of the present disclosure, an operation performed bythe PDCP reception device when a bearer is reconfigured will bedescribed.

Reconfiguration of a bearer may refer to, for example, a case where anMCG bearer is reconfigured into a multi-bearer, a multi-bearer isreconfigured into an MCG bearer, or a multi-bearer is reconfigured intoa multi-bearer.

During the bearer reconfiguration, the UE may apply a PDCP operation 9and a PDCP operation 10 alternately or sequentially.

Reference will be made to Table 8 below to describe examples of the PDCPoperation 9 and the PDCP operation 10.

TABLE 8 PDCP operation 9: operation PDCP operation 10: operation forsingle bearer for multi-bearer PDCP PDU reception PDCP PDU receptionDetermine HFN/COUNT Determine HFN/COUNT of PDCP PDU. Process of PDCPPDU. Discard PDU received in duplicate PDU received in duplicate withoutinto PDCP SDU, and then processing it into PDCP SDU. discard PDUreceived in duplicate Process PDCP PDU into PDCP SDU Deliver PDCP PDUsProcess PDCP PDU satisfying upper satisfying condition layer deliverycondition 7 into PDCP in Table 9 to the SDU, and deliver PDCP SDU to theupper layer, if received upper layer. Store PDCP PDUs PDU is first PDU.Deliver unsatisfying upper layer delivery PDCP PDUs satisfying condition7 in the buffer, and perform condition in Table 10 to the timer-basedreordering operation. If upper layer, if received timer 3 expires,process in-sequence PDU is second PDU. PDCP PDUs into PDCP SDUs based onReordering_PDCP_RX_COUNT, and deliver PDCP SDUs to the upper layer.

TABLE 9 all stored PDCP SDU(s) with consecutively associated COUNTvalue(s) starting from the COUNT value associated with the received PDCPSDU;

TABLE 10 all stored PDCP SDU(s) with an associated COUNT value less thanthe COUNT value associated with the received PDCP SDU; all stored PDCPSDU(s) with consecutively associated COUNT value(s) starting from theCOUNT value associated with the received PDCP SDU;

Since the expression that the condition in Table 9 is satisfied meansthat a received PDCP PDU is a missing PDCP PDU (e.g., received PDCPSN=Last_Submitted_PDCP_RX_SN+1) with the lowest sequence number, anin-sequence PDCP PDU may occur as the PDU is received.

A PDCP PDU for which the condition in Table 10 is satisfied may refer toall missing PDUs with sequence numbers lower than that of the receivedPDCP PDU and sequentially received PDCP PDUs, including the missing PDCPPDU.

In Table 8, a first PDU may be a PDCP PDU that is received due to thereestablishment or release of a lower layer, and may occur during ahandover. In other words, if a handover is instructed, out-of-sequencePDCP PDUs stored in the RLC layer may be delivered to the PDCP device,and these PDCP PDUs will be referred to as the ‘first PDU’.

In Table 8, a second PDU may be a PDCP PDU that is received neither dueto the reestablishment of a lower layer, nor due to the release of alower layer, and the second PDU may be PDCP PDUs that are received froma target cell after a handover is completed.

On the basis of a handover, the first PDU may be construed as anout-of-sequence PDCP PDU received from the source cell, and the secondPDU may be construed as a PDCP PDU received from the target cell.

In an embodiment of the present disclosure, an MeNB may reconfigure aspecific bearer or instruct a handover, using an RRC connectionreconfiguration control message. In this case, a UE may perform anoptimized operation depending on the type of reconfiguration indicatedin the RRC connection reconfiguration message.

FIG. 29 illustrates a UE operation during a bearer reconfigurationaccording to an embodiment of the present disclosure.

Referring to FIG. 29, in operation 2905, the UE may receive a bearerreconfiguration message related to a multi-bearer. In this embodiment,the wording ‘related to a multi-bearer’ means that a multi-bearer ischanged to, for example, an MCG bearer or a multi-bearer, or an MCGbearer is changed to a multi-bearer, using the control message.

In operation 2910, the UE may determine whether a handover isinstructed, using the control message. If a handover is instructed, thePDCP may perform a reconfiguration operation. The PDCP reconfigurationmay include specific operations such as applying a new security key andresetting a header compression operation, and may be performed duringthe handover.

If a handover is not instructed, the UE may proceed to operation 2915,and if a handover is instructed, the UE may proceed to operation 2935.

In operation 2915, the UE may check the type of reconfiguration. If thereconfiguration type indicates reconfiguration from an MCG bearer to amulti-bearer, the UE may proceed to operation 2920. If thereconfiguration type indicates reconfiguration from a multi-bearer to amulti-bearer, the UE may proceed to operation 2925. If thereconfiguration type indicates reconfiguration from a multi-bearer to anMCG bearer, the UE may proceed to operation 2930.

In operation 2935, the UE may check the type of reconfiguration. If thereconfiguration type indicates reconfiguration from an MCG bearer to amulti-bearer, the UE may proceed to operation 2940. If thereconfiguration type indicates reconfiguration from a multi-bearer to amulti-bearer, the UE may proceed to operation 2945. If thereconfiguration type indicates reconfiguration from a multi-bearer to anMCG bearer, the UE may proceed to operation 2950.

In operation 2920, the UE may stop applying the PDCP operation 9, andthen apply the PDCP operation 10. In other words, the UE has received anRRC connection reconfiguration message related to a multi-bearer, andwhen the reconfiguration is performed, if the PDCP is not reconfigured(i.e., the reconfiguration is not the reconfiguration that is performedwith the handover) and an MCG bearer is reconfigured into amulti-bearer, then the UE may stop applying the PDCP operation 9 whichis an operation for an MCG bearer, and then apply the PDCP operation 10which is an operation for a multi-bearer.

In operation 2925, the UE may continue to apply the PDCP operation 10.In other words, the UE has received an RRC connection reconfigurationmessage related to a multi-bearer, and when the reconfiguration isperformed, if the PDCP is not reconfigured (i.e., the reconfiguration isnot the reconfiguration that is performed with the handover) and amulti-bearer is reconfigured into a multi-bearer, then the UE maycontinue to apply the PDCP operation 10 which is an operation for amulti-bearer.

In operation 2930, the UE may apply the PDCP operation 10 until apredetermined condition is satisfied. The predetermined condition may besatisfied when the PDCP is first reconfigured after the bearerreconfiguration is completed. In other words, the UE has received an RRCconnection reconfiguration message related to a multi-bearer, and whenthe reconfiguration is performed, if the PDCP is not reconfigured (i.e.,the reconfiguration is not the reconfiguration that is performed withthe handover) and a multi-bearer is reconfigured into an MCG bearer,then the UE may continue to apply the PDCP operation 10 which is anoperation for a multi-bearer, even though the bearer is reconfiguredinto an MCG bearer. If the PDCP is reconfigured, the UE may apply thePDCP operation 9 which is an operation for an MCG bearer (i.e., the UEmay continue to apply the PDCP operation 10 until a handover isinstructed after the reconfiguration to an MCG bearer is completed, andif the handover is instructed, the UE may apply the PDCP operation 9).

The reason why the UE does not immediately apply the PDCP operation 9 inoperation 2930 is that since there may be out-of-sequence PDCP PDUs ifthe bearer is reconfigured from a multi-bearer to an MCS bearer, the UEshould continue to apply the PDCP operation 10 until the out-of-sequencePDUs are in sequence, in order to prevent the data loss.

In operation 2940, the UE may apply the PDCP operation 9 for first PDUs,and apply the PDCP operation 10 for second PDUs. As described above, thefirst PDUs may refer to PDCP PDUs received from the source cell, and ifthe PDCP operation 10 is applied even for the first PDUs, degradation ofthe reordering performance may occur. The second PDUs may refer to PDUsreceived from the target cell, and the second PDUs may be received afterthe first PDUs are received all. Since the second PDUs are receivedafter the reconfiguration to a multi-bearer is completed, the UE mayapply the PDCP operation 10 for the second PDUs. In other words, the UEhas received an RRC connection reconfiguration message related to amulti-bearer, and when the reconfiguration is performed, if the PDCP isalso reconfigured together (i.e., the reconfiguration is thereconfiguration that is performed with the handover) and a multi-beareris reconfigured into an MCG bearer, then the UE may apply the PDCPoperation 9 for the PDCP PDUs that have been received by thereconfiguration/release of the lower layer, and apply the PDCP operation10 for the PDCP PDUs that have not been received by thereconfiguration/release of the lower layer.

In operation 2945, the UE may apply the PDCP operation 9 for the firstPDUs and apply the PDCP operation 10 for the second PDUs, like inoperation 2940. In other words, the UE has received an RRC connectionreconfiguration message related to a multi-bearer, and when thereconfiguration is performed, if the PDCP is also reconfigured together(i.e., the reconfiguration is the reconfiguration that is performed withthe handover) and a multi-bearer is reconfigured into a multi-bearer,then the UE may apply the PDCP operation 9 for the PDCP PDUs that havebeen received by the reconfiguration/release of the lower layer, andapply the PDCP operation 10 for the PDCP PDUs that have not beenreceived by the reconfiguration/release of the lower layer.

In operation 2950, the UE may apply the PDCP operation 9 for both of thefirst PDUs and the second PDUs. In other words, the UE has received anRRC connection reconfiguration message related to a multi-bearer, andwhen the reconfiguration is performed, if the PDCP is also reconfiguredtogether (i.e., the reconfiguration is the reconfiguration that isperformed with the handover) and a multi-bearer is reconfigured into anMCG bearer, then the UE may apply the PDCP operation 9 for the PDCP PDUsthat have been received by the reconfiguration/release of the lowerlayer, and apply the PDCP operation 9 even for the PDCP PDUs that havenot been received by the reconfiguration/release of the lower layer. Inother words, the UE may immediately apply the PDCP operation.

In an embodiment of the present disclosure, an operation may beproposed, in which a PDCP reception device processes PDCP PDUs receivedfrom a lower layer.

In this embodiment of the present disclosure, if a PDCP PDU is receivedfrom the lower layer, the PDCP reception device may determine whetherthe PDU satisfies a predetermined duplicate reception condition, andtake a predetermined action for the PDU satisfying the duplicatereception condition. The PDCP reception device may perform differentoperations depending on whether the PDCP reception device is a deviceconnected with a single bearer, or a device connected with amulti-bearer.

The duplicate reception condition for an arbitrary PDU may be defined asshown in Table 11 below.

TABLE 11 if received PDCP SN - Last_Submitted_PDCP_RX_SN >Reordering_Window, or 0 ≤ Last_Submitted_PDCP_RX_SN - received PDCP SN <Reordering_Window:

The duplicate reception condition is for determining whether a sequencenumber of a received PDU is a number lower thanLast_Submitted_PDCP_RX_SN (or whether a sequence number of a receivedPDU is a number (e.g., an older number) that is assigned earlier thanLast_Submitted_PDCP_RX_SN), instead of determining whether an arbitraryPDCP PDU has been received before, and the duplicate reception conditionmay be for determining whether a sequence number of a received PDU is asequence number lower than the lowest sequence number that has alreadybeen delivered to the upper layer.

The expression that the duplicate reception condition is satisfied foran arbitrary PDCP PDU means that since a payload of the PDCP PDU ishighly likely to be already delivered to the upper layer, theunnecessary malfunction is highly likely to occur if a PDCP SDU isdelivered to the upper layer. Therefore, in this embodiment, the PDCPreception device may discard the PDCP PDU satisfying the duplicatereception condition, without delivering it to the upper layer.

If the PDCP PDU satisfying the duplicate reception condition is a PDCPPDU that has been received on a single bearer, the UE may perform anoperation of processing the PDCP PDU into a PDCP SDU to update a RobustHeader Compression (ROHC) context (see RFC 3095) before discarding thePDCP PDU, and then discard the PDCP SDU. On the other hand, if the PDCPPDU satisfying the duplicate reception condition is a PDCP PDU that hasbeen received on a multi-bearer, the UE may immediately discard the PDCPPDU without processing the PDCP PDU into an SDU. The reason for applyingdifferent operations as described above is as follows.

If the PDCP PDU satisfying the duplicate reception condition is a PDCPPDU that has been received on a single bearer, even though the PDCP PDUis a PDU received in duplicate, an important packet related to ROHC maybe included in the PDCP PDU. This phenomenon may occur if ROHC is resetin the process such as handover. Therefore, even though the PDCP PDUreceived on a single bearer is a PDCP PDU received in duplicate, the UEmay first process the PDCP PDU into a PDCP SDU to update the ROHCcontext, and then discard the PDCP SDU.

In the multi-bearer operation, since ROHC is not reset, it is notnecessary for the UE to perform the operation of processing the packetreceived in duplicate to update the ROHC context. Therefore, the UE mayimmediately discard the PDCP PDU, if it is determined that the PDCP PDUis received in duplicate.

FIG. 27 illustrates an operation of determining whether a UE hasreceived, in duplicate, a PDCP PDU according to an embodiment of thepresent disclosure.

Referring to FIG. 27, in operation 2705, the PDCP reception device mayreceive a PDCP PDU from a lower layer. In operation 2710, the PDCPreception device may determine whether a sequence number of the PDCP SDUsatisfies the duplicate reception condition. If the sequence number ofthe PDCP SDU does not satisfy the duplicate reception condition, thePDCP reception device may proceed to operation 2715, and if the sequencenumber of the PDCP SDU satisfies the duplicate reception condition, thePDCP reception device may proceed to operation 2720. In operation 2715,the PDCP reception device may determine whether the received PDCP PDU isdelivered from a multi-bearer or from a single bearer. If the receivedPDCP PDU is delivered from a multi-bearer, the PDCP reception device mayproceed to operation 2719, and if the received PDCP PDU is deliveredfrom a single bearer, the PDCP reception device may proceed to operation2717.

In operation 2717, the UE may process the received PDCP PDU into a PDCPSDU, without considering whether the received PDCP PDU is reordered, andthen deliver the PDCP SDU to the upper layer. In operation 2719, if thereceived PDCP PDU is in sequence, the UE may immediately process thePDCP PDU into a PDCP SDU and then deliver the PDCP SDU to the upperlayer, and if the received PDCP PDU is not in sequence (or is out ofsequence), the UE may process the PDCP PDU into a PDCP SDU, afterreordering of the PDCP PDU is completed, and then deliver the PDCP SDUto the upper layer. In other words, in operation 2719, the UE mayprocess only the PDCP PDU, reordering of which is completed, into a PDCPSDU, and deliver the PDCP SDU to the upper layer. Here, processing aPDCP PDU into a PDCP SDU may mean converting a PDCP PDU into a PDCP SDUby performing an operation such as deciphering a PDCP PDU anddecompressing a header thereof.

If the duplicate reception condition is satisfied in operation 2710, thePDCP reception device may determine in operation 2720 whether the bearerfrom which the PDCP PDU is delivered is a single bearer or amulti-bearer. If the bearer is a single bearer, the PDCP receptiondevice may proceed to operation 2725, and if the bearer is amulti-bearer, the PDCP reception device may proceed to operation 2730.In operation 2725, the PDCP reception device may process the PDCP PDUinto a PDCP SDU, and then discard the PDCP SDU. In operation 2730, thePDCP reception device may discard the PDCP PDU without processing thePDCP PDU into a PDCP SDU.

In the example of FIG. 27, as another operation of the UE, if a PDCPPDU, a half PDCP SDU or a PDCP SDU having the same sequence number asthat of the received PDCP PDU is already stored in the PDCP receptionbuffer, the UE may perform different operations for a single bearer anda multi-bearer.

For example, if a PDCP SDU with the same sequence number as that of thereceived PDCP PDU is already stored in the PDCP reception buffer of asingle bearer, the UE may decipher the PDCP PDU, decompress its header,and then discard the PDCP PDU. The reason for discarding the PDCP PDUafter decompressing its header is to update the header decompressioncontext by decompressing the header because the PDCP PDU transmitted induplicate is highly likely to be a packet, a header of which iscompressed as a more recent header compression context.

In addition, if a PDCP SDU, a half PDCP SDU or a PDCP PDU having thesame sequence number as that of the received PDCP PDU is already storedin the PDCP reception buffer of a multi-bearer, the UE may decipher thePDCP PDU, process the deciphered PDCP PDU into a half PDCP SDU, and thendiscard the currently stored PDCP packet (e.g., PDCP PDU, half PDCP SDUor PDCP SDU) with the same sequence number, and store the half PDCP SDU.

In the case of a multi-bearer, if a header of an out-of-sequence halfPDCP SDU is decompressed, header decompression of its subsequent halfPDCP SDUs may be affected. Therefore, as described above, the UE maystore the packet received in duplicate until the packet received induplicate is reordered, without decompressing a header thereof.

Although not shown in the example of FIG. 27, as another operation ofthe UE, if a PDCP PDU or a PDCP SDU having the same sequence number asthat of the received PDCP PDU is already stored in the PDCP receptionbuffer of a multi-bearer, the UE may perform another differentoperation.

For example, if a PDCP SDU with the same COUNT as COUNT of the receivedPDCP PDU is already stored in the PDCP reception buffer of amulti-bearer, the UE may decipher the PDCP PDU, decompress a headerthereof, and then discard the PDCP PDU. The reason for discarding thePDCP PDU after decompressing its header is to update the headerdecompression context by decompressing the header because the PDCP PDUtransmitted in duplicate is highly likely to be a packet, a header ofwhich is compressed as a more recent header compression context.

In addition, if a PDCP PDU with the same COUNT as COUNT of the receivedPDCP PDU is already stored in the PDCP reception buffer of amulti-bearer, the UE may discard the stored PDCP PDU and store a newlyreceived PDCP PDU. In the case of a single bearer, the reason forperforming an operation different from the operation of discarding aPDCP PDU received in duplicate is that in the multi-bearer structure, inretransmitting a predetermined PDCP PDU, the UE may compress again aheader as a more recent header compression context, and then retransmitthe PDCP PDU. As another operation of the UE, in processing a PDCPpacket (e.g., PDCP PDU or PDCP SDU) with the same COUNT as that of thereceived PDCP PDU, the UE may perform a different operation depending onwhether the PDCP packet with the same COUNT is a PDCP SDU or a PDCP PDU.

If a PDCP packet with the same COUNT as COUNT of the received PDCP PDUis already stored, the UE may determine whether the stored PDCP packetis a PDCP PDU or a PDCP SDU, and if the stored PDCP packet is a PDCPPDU, the UE may discard the PDCP PDU without performing an additionaloperation. On the other hand, if the stored PDCP packet is a PDCP SDU,the UE may decompress a header of the received PDCP PDU, decipher thePDCP PDU, and then discard the PDCP PDU.

Now, a description will be made of a method for setting a PrioritizedBit Rate (PBR) for a multi-bearer according to an embodiment of thepresent disclosure.

In transmitting data using an uplink grant assigned by an ENB, a UE maydetermine which data the UE will transmit, taking into account thepriority of a logical channel. If data is continuously generated in ahigh-priority logical channel, data of a low-priority logical channelmay not be serviced for a long time, causing the problem that theminimum data transmission/reception for keeping a data session is alsoimpossible. In order to solve this problem, the concept of PBR has beenintroduced. If PBR is set in a logical channel, the UE may increase aPBR-related token Bj by PBR for the logical channel in everyTransmission Time Interval (TTI). In determining data to transmit, theUE may first consider the Bj. For example, even though transmittabledata is present in a high-priority logical channel x, if Bj of thelogical channel x is 0, the UE may preferentially transmit data of alogical channel, priority of which is low but Bj of which is not 0, byat least Bj. This operation follows the description in Section 5.7 ofthe standard TS36.321.

The PBR may be assigned and managed for each logical channel. However,if the logical channel is a local channel connected to a multi-bearer,it is preferable to operate the PBR taking into all the related logicalchannels, instead of independently operating the PBR for each logicalchannel. The reason is that the purpose of the PBR is to ensure theminimum transmission bandwidth for an arbitrary data service, and in thecase of a multi-bearer, one service is related to two logical channels.

In the existing signaling system, parameters related to PBR may includeprioritisedBitRate and bucketSizeDuration, and the parameters may besignaled for each logical channel. Bj is first initialized to zero (0),and then increases by prioritisedBitRate in every TTI. The maximum sizeof Bj is limited to a product of prioritisedBitRate andbucketSizeDuration. Generally, a specific radio bearer may be configuredas a single bearer that is connected only with one logical channel. Ifthe UE moves to a macro-cell area in the future, the single bearer maybe reconfigured into a multi-bearer, and the UE may properly distributePBRs of the multi-bearer to an SCG logical channel and an MCG logicalchannel according to a predetermined rule.

FIG. 12 illustrates a UE's operation of setting a PBR for a multi-beareraccording to an embodiment of the present disclosure.

Referring to FIG. 12, in operation 1205, the UE may receive a controlmessage for instructing to reconfigure a single bearer into amulti-bearer. In operation 1210, the UE may adjust a PBR of an MCGlogical channel and a PBR of an SCG logical channel to appropriatevalues, referring to PBR information of a control message 1 and acontrol message 2. The control message 2 means a control message forreconfiguring a single bearer into a multi-bearer, and the controlmessage 1 means a control message containing PBR information about thesingle bearer. Typically, the control message 1 may be generated first,and the control message 2 may be generated later. There may be severalmethods for adjusting PBRs of the MCG logical channel and the SCGlogical channel, and one of the methods presented below can be used.

PBR Setting Method 1 for Arbitrary Multi-Bearer x

If PBR of a logical channel of a bearer x is set as A in the controlmessage 1 and PBR of an SCG Logical Channel (LCH) of a bearer x is setas B in the control message 2, PBR of the SCG LCH may be set as asignaled B and PBR of the MCG LCH may be adjusted to A-B.

PBR Setting Method 2 for Arbitrary Multi-Bearer x

If PBR information is present in the control message 2, PBR may beapplied to an SCG LCH, and if PBR information is not present, PBR may beapplied to an MCG LCH. In other words, if PBR of a logical channel of abearer x is set as A in the control message 1 and PBR of an SCG LCH of abearer x is set as B in the control message 2, PBR of the SCG LCH may beset as a signaled B and PBR of the MCG LCH may be adjusted to zero (0).Otherwise, if PBR for the SCG LCH of the bearer x is not set in thecontrol message 2, PBR of the MCG LCH may be kept as A, and PBR of theSCG LCH may be set to 0.

PBR Setting Method 3 for Arbitrary Multi-Bearer x

An LCH to which PBR is to be applied may be specified through thecontrol message 2. For example, PBR may be set as shown in Table 12below.

TABLE 12 PBR of LCH PBR of LCH PBR of bearer x of bearer x indicator incontrol in control of control PBR of MCG LCH message 1 message 2 message2 and SCG LCH A B SCG MCG LCH PBR = 0 SCG LCH PBR = B A B MCG MCG LCHPBR = B SCG LCH PBR = 0 A Absent Absent MCG LCH PBR = A SCG LCH PBR = 0A Absent SCG MCG LCH PBR = 0 SCG LCH PBR = A

For example, if PBR of a logical channel of a bearer x is notified as Ain the control message 1 and PBR of a logical channel of a bearer x isset as B and a PBR indicator is set as MCG in the control message 2, theUE may adjust PBR of the MCG LCH to B and set PBR of the SCG LCH to 0.In operation 1215, the UE may shift a predetermined amount of Bj of theexisting MCG LCH to the SCG LCH.

If the PBR setting method 1 is used, the UE may subtract a predeterminedratio of Bj for the MCG LCH, from the MCG LCH, and add it to the SCGLCH. Therefore, Bj of the SCG LCH may be initialized to the amount of Bjthat is shifted in the MCG LCH, instead of being initialized to 0.

If the PBR setting method 2 or 3 is used, in a case where PBR is appliedto the SCG, the whole of Bj of the MCG LCH may be shifted to the SCGLCH. If PBR is applied to the MCG, Bj of the MCG LCH may be kept intact.

In operation 1220, the UE may perform an operation related to PBR in theMCG LCH and the SCG LCH by applying the adjusted PBR and the adjustedBj. In other words, the UE may perform an operation of increasing Bj byPBR in every TTI, and decreasing Bj as much as the amount of datatransmitted.

Although it is assumed in various embodiments of the present disclosurethat the MCG serving cell and the SCG serving cell both use the LTEtechnology, the two cell groups may use different wireless technologies.For example, the UE may exchange data with the MCG serving cell, usingthe LTE wireless technology, and may exchange data with the SCG servingcell, using another wireless technology (e.g., Wireless Fidelity (WiFi)technology or High Speed Packet Access (HSPA) technology). In thescenario where the UE transmits and receives data using differentwireless technologies together, one PDCP device may perform reorderingon the PDCP PDUs that are received through different wirelesstechnologies, and distribute the PDCP PDUs to lower layer devices thatuse different wireless technologies. In this case, it is possible toapply the technologies (e.g., the timer-based reordering technology orthe reordering operation switching procedure) presented throughout thisspecification. Herein, the multi-bearer may be defined as a bearer, inwhich one PDCP device is connected with two lower layers that usedifferent wireless technologies and at least one of them is a lowerlayer that uses the LTE technology.

Now, a description will be made of a method in which an RLC device of aUE requests retransmission of a missing packet according to anembodiment of the present disclosure.

If a predetermined event occurs, the RLC reception device may generatean RLC STATUS PDU to report a sequence number of a normally received RLCPDU, and request retransmission of an RLC PDU, or some (e.g., an RLC PDUsegment) of the RLC PDU, the RLC PDU or the RLC PDU segment beingrequired to be retransmitted. For a normal operation of the RLC, the RLCreception device may follow the 3GPP standard TS36.322, and an RLC PDUmay be interchangeably used with an Acknowledged Mode Data (AMD) PDU.

The RLC STATUS PDU may be significantly large in size depending on theradio channel conditions, and the UE may not transmit the whole RLCSTATUS PDU with given transmission resources. In this case, the UE mayoptionally report only the information that is reportable in the giventransmission resources.

For example, the reception status of a UE will be assumed to be as shownbelow.

-   -   Highest RLC sequence number received so far=100    -   Missing RLC PDUs=90 and 95    -   Missing RLC PDU segment=from 100th byte to 150th byte of a PDU

A STATUS PDU may be configured with one ACK_SN, one or more NACK_SNs,zero (0) per NACK_SN, and one or more SOstart/SOend pairs, as shown inthe example of FIG. 13 showing a format of the STATUS PDU. A STATUS PDUthat should be configured in the above condition may be as follows, andthe size of the STATUS PDU may be 101 bits.

-   -   ACK_SN=101    -   NACK_SN=90    -   NACK_SN=93; SOstart=100; SOend=150    -   NACK_SN=95

If the amount of transmission resources to be allocated to the RLCdevice is, for example, 16 bits, the UE may configure a STATUS PDU asshown below according to the amount of possible transmission resources.

-   -   ACK_SN=90

In other words, the UE may report only the information indicating thatthe UE has normally received up to the sequence number 89, and may notreport on the remaining RLC PDUs.

In some cases, if the UE reports only some information as above,incorrect information may be transmitted.

FIG. 13 illustrates a format of a status PDU according to an embodimentof the present disclosure.

Referring to FIG. 13, several SOstart/SOend pairs may be contained forone NACK_SN, and if only part of the information is contained due to theamount of given transmission resources, the RLC device that has receivedthe STATUS PDU may make a wrong determination. For example, thereception status of the RLC reception device at an arbitrary time may beas follows.

-   -   Highest RLC sequence number received so far=100    -   Missing RLC PDU segment=from 100th byte to 150th byte of a PDU        [93], and from 180th byte to the last bytes of a PDU [93].

In other words, some (e.g., 1st˜99th bytes and 151st˜179th bytes) of theRLC PDU with a sequence number 93 has been normally received, and theother (e.g., 100th˜150th bytes and 180th˜the last bytes) of the RLC PDUwith a sequence number 93 has not been normally received.

If the amount of transmission resources that the UE can use at the timean RLC STATUS PDU is triggered is only enough to include ACK_SN, NACK_SNand one SOstart/SOend pair, the UE may generate and transmit thefollowing STATUS PDU.

-   -   ACK_SN=100    -   NACK_SN=93; SOstart=100; SOend=150

The RLC device that has received the STATUS PDU may discard the part of180th˜the last bytes of the RLC PDU with a sequence number 93 from thebuffer, misjudging that the UE has normally received even the part of180th˜the last bytes. An operation of the RLC reception device forsolving this problem will be described with reference to FIG. 14.Referring to other fields in FIG. 13, D/C field indicates whether thePDU is data PDU or control PDU, CPT (Control PDU Type) field indicatesthe type of the control PDU, E1 (Extension bit 1) field indicateswhether a set of NACK_SN, E1, and E2 follow, and E2 (Extension bit 2)field indicates whether a set of SOstart and SOend follows. Oct 1 to Oct9 indicate octets.

FIG. 14 illustrates an operation of an RLC reception device generating astatus PDU according to an embodiment of the present disclosure.

Referring to FIG. 14, an RLC STATUS PDU may be triggered in operation1405. The RLC STATUS PDU may be triggered if a t-Reordering timerexpires in a situation where t-StatusProhibit is not driven, or if afirst transmission opportunity occurs after an RLC PDU in which a pollbit is set is received.

In operation 1410, the RLC reception device may determine whether it cangenerate a STATUS PDU including all of ACK_SN, NACK_SN and SOstart/SOendthat reflect the current reception status in the transmissionopportunity, (e.g., determine whether the size of STATUS REPORT in whichall the current statuses are reflected is less than the size of thetransmittable RLC PDU). If so, the RLC reception device may proceed tooperation 1415, and if not so, the RLC reception device may proceed tooperation 1420.

In operation 1415, the UE may generate a STATUS PDU by writing ACK_SN,NACK_SN and SOstart/SOend therein so as to reflect the reception statusat that time.

In operation 1420, the UE may determine whether the following Conditionis satisfied. If the Condition is satisfied, the UE may proceed tooperation 1425, and if the Condition is not satisfied, the UE mayproceed to operation 1430.

Condition

When the UE generates a STATUS PDU according to the amount of giventransmission resources (or the size of an RLC PDU provided by a lowerlayer), is only some of one or more SOstart/SOend pairs for one NACK_SNincluded in the STATUS PDU? In other words, can the UE report thereception status only for some segments with respect to the RLC PDU, oneor more segments of which have not been received? In other words, canonly some of several SOstart/SOend pairs be included?

In operation 1425, the RLC reception device may set a SOend value of thelast SOstart/SOend pair included in the NACK_SN to a predetermined value(e.g., “111111111111111”). If SOend is set to the above value, it meansthat the RLC reception device has not received the part from the byteindicated by the SOstart to the last byte. In other words, by setting avalue of the last SOend to the above value, the RLC reception device mayrequest transmission even for the successfully received segment, and mayat least prevent the RLC transmission device from discarding the segmentthat the RLC transmission device has not received yet. In the aboveexample, the following STATUS PDU may be generated.

-   -   ACK_SN=100    -   NACK_SN=93; SOstart=100; SOend=predetermined value

The transmission device that has received the STATUS PDU may not discard151st˜179th bytes of an RLC PDU with a sequence number 93.

As another operation, in operation 1425, the RLC reception device maycancel the triggered STATUS PDU, and trigger again a STATUS PDU in thenext transmission opportunity. In other words, this is because in thenext transmission opportunity, more transmission resources may beallocated, making it possible to include all the necessary information.

In operation 1430, the UE may determine up to which RLC PDU segment theUE will report NACK information according to the size of the RLC PDU,write in ACK_SN the sequence number of a missing RLC PDU following thelast RLC PDU segment, and generate a STATUS PDU by sequentially writingan RLC PDU given to report NACK information, or NACK information for theRLC PDU segment. An operation of the RLC transmission device for solvingthis problem will be described with reference to FIG. 15.

FIG. 15 illustrates an operation of an RLC transmission device receivinga status PDU according to an embodiment of the present disclosure.

Referring to FIG. 15, the RLC transmission device may receive/trigger aSTATUS PDU in operation 1505.

In operation 1510, the RLC transmission device may determine which RLCPDU and RLC PDU segment have been normally transmitted, using ACK_SN,NACK_SN, SOstart and SOend of the STATUS PDU, and may discard thenormally transmitted packets from its transmission buffer and prepare toretransmit the packets, retransmission of which is required. In thiscase, the RLC transmission device may determine the data to be discardedfrom the transmission buffer, and the data to be retransmitted, asfollows. Hereinafter, for convenience of description, NACK informationconfigured with one NACK_SN and one or more SOstart/SOend pairs will bereferred to as partial NACK information. An element containingmeaningful information such as ACK_SN, NACK_SN, NACK_SN andSOstart/SOend will be referred to as a STATUS element.

The RLC transmission device may determine that it should retransmit allthe RLC PDUs that are indicated only with NACK_SN in the STATUS PDU.

The RLC transmission device may determine that it should retransmit theRLC PDU segments that are reported to be missing by the partial NACKinformation included in the STATUS PDU.

The RLC transmission device may determine that the remaining segmentsexcept for the RLC PDU segments that are reported to be missing by thepartial NACK information, other than the last STATUS element, in thepartial NACK information included in the STATUS PDU, have been normallyreceived, and discard the remaining segments.

If the last STATUS element of the STATUS PDU is partial NACKinformation, the RLC transmission device may not determine whether theremaining segments except for the RLC PDU segments that are reported tobe missing by the partial NACK information have been received or not. Inother words, the RLC transmission device may neither discard theremaining segments nor retransmit the remaining segments.

Now, a description will be made of a method in which a UE reports aplurality of categories and performs an HARQ operation by applying oneof the categories according to an embodiment of the present disclosure.

In order for a UE and an ENB to perform data exchange, the ENB shouldrecognize the capability of the UE. For example, information such as theUE's maximum downlink data rate and the UE's HARQ buffer performance maybe the information that the ENB should be aware of in order to transmitdownlink data to the UE. The capability information related to the UE'sdownlink data transmission/reception may be reported to the ENB in theform of a UE category. The following table shows the ‘UE category’defined in the standard 36.306. If the UE categories are classifiedbased on the UE's downlink data reception capability, category 1corresponds to 10 Mbps, category 2 corresponds to 50 Mbps, category 3corresponds to 100 Mbps, category 4 corresponds to 150 Mbps, andcategories 5, 6 and 7 correspond to 300 Mbps, and category 8 correspondsto 3 Gbps.

TABLE 13 Maximum number Total number Maximum of bits that UE of softnumber of UE can receive within channel bits supportable Category oneTTI (1 ms) (Buffer size) downlink layers Category 1 10296 250368 1Category 2 51024 1237248 2 Category 3 102048 1237248 2 Category 4 1507521827072 2 Category 5 299552 3667200 4 Category 6 301504 3667200 2Category 6′ 301504 3667200 4 Category 7 301504 3667200 2 Category 7′301504 3667200 4 Category 8 2998560 35982720 8

In Table 13, the categories 1˜5 have been introduced in LTE StandardRelease 8, and the categories 6˜8 have been introduced in LTE StandardRelease 10. In other words, a Release 8-based ENB may not understand thecategories 6˜8. The introduction of categories corresponding to otherdata rates in addition to the above categories may be required. Forexample, in LTE standard Release 12, the introduction of new categories9 and 10 corresponding to 450 Mbps has been determined. Hereinafter, forconvenience of description, the categories 1˜5 will be referred to as afirst category, the categories 6˜8 will be referred to as a secondcategory, and the categories 9˜10 will be referred to as a thirdcategory. An ENB based on Release 8 and Release 9 may not understand thesecond category and the third category, an ENB based on Release 10 andRelease 11 may not understand the third category, and an ENB based onRelease 12 or later Release may understand all the categories. A UE mayreport several categories in some cases, since the UE cannot recognizethe Release of the ENB. For example, a UE of the second category mayreport not only the second category but also the first categorytogether. A UE of the third category may report not only the thirdcategory but also the second category and the first category together.Since the categories have a close relationship with the size of a softbuffer as described below, the UE and the ENB should apply the samecategory each other. Therefore, there is a need for a method in whichthe UE and the ENB apply the same categories for the UE that hasreported a plurality of categories. Each item of the table will bedescribed in more detail below.

In the table, by multiplying ‘maximum number of bits that UE can receivewithin one TTI (1 ms)’ by 1000, it is possible to convert the maximumnumber of bits into the maximum transfer rate per second of the system.

In the table, ‘total number of soft channel bits’ may not only berelated to the buffer size of the UE, but also affect the rate matchingoperation. If ‘total number of soft channel bits’ is defined as Nsoft,‘soft buffer size for transport block’ is defined asNoise-to-Interference Ratio (N_(IR)), and ‘soft buffer size for codeblock’ is defined as Ncb, a relationship of Equation (1) below may begiven.

$\begin{matrix}{{N_{IR} = \left\lfloor \frac{N_{soft}}{K_{MIMO} \cdot {\min\left( {M_{{DL}_{—}{HARQ}},M_{limit}} \right)}} \right\rfloor},{N_{cb} = {\min\left( {\left\lfloor \frac{N_{IR}}{C} \right\rfloor,K_{w}} \right)}}} & {{Equation}\mspace{14mu}(1)}\end{matrix}$

Where K_(MIMO) has a value of 2 or 1 depending on the transmission mode,and min(M_(DL) _(_) _(HARQ), M_(limit)) generally has a value of 8. Inaddition, C represents the number of code blocks, and K_(W) represents alength of a circular buffer and has a relationship of K_(W)=3KΠ where KΠrepresents an interleaver size of a sub block and has a length of 6144bits. In other words, as shown in the above Equation, it can beunderstood that if a value of Nsoft affects a value of the N_(IR) and avalue of N_(IR)/C is less than K_(W), (in other words, if a high-speeddata transmission/reception is in progress), the value of the N_(IR)affects a value of Ncb. Since a puncturing/repetition pattern isaffected depending on the value of Ncb, it can be understood that if avalue of Nsoft between a UE and an ENB is misunderstood, it may cause awrong operation. Other various matters related to, for example, ratematching may follow the standard 36.212.

FIG. 18 illustrates an ENB's operation of performing downlink datatransmission/reception with a UE that has reported three categoriesaccording to an embodiment of the present disclosure.

Referring to FIG. 18, in a mobile communication system including a UE1805, an ENB 1810 and an MME 1815, the UE 1805 may be powered on inoperation 1820. The UE 1805 may perform cell search, and if anaccessible cell is detected, the UE 1805 may perform an RRC connectionestablishment procedure (see the standard 36.331) with the ENB 1810through the cell, in operation 1825. In operation 1830, the UE 1805 maysend a predetermined control message to the MME 1815 through theestablished RRC connection. The control message may be, for example, aservice request message for requesting initiation of a service, or anattach request message for requesting initial registration. The MME 1815may determine whether to accept the request of the UE 1805 through apredetermined procedure, and if the MME 1815 determines to provide amobile communication service to the UE 1805, accepting the request, theMME 1815 may send a control message containing information related tothe UE 1805 to the ENB 1810 in operation 1835. The control message mayinclude the information (e.g., security key information, the UE'sservice profile information, etc.) that the ENB 1810 requires in orderto perform data transmission/reception with the UE 1805. If the MME 1815has capability information of the UE 1805, the MME 1815 may include eventhe capability information of the UE 1805 in the control message. If theMME 1815 does not have capability information of the UE 1805, thecapability information may not be delivered to the ENB 1810, and the ENB1810 may send a predetermined RRC control message to the UE 1805 inorder to obtain the capability information of the UE 1805 in operation1840. The control message refers to a UE capability information requestmessage or (a UE capability enquiry message), and the control messagemay contain or have a field indicating capability information of which aRadio Access Technology (RAT) the ENB 1810 requests. The LTE ENB 1810may set the field so that capability information for Evolved UniversalTerrestrial Radio Access (E-UTRA) may be requested. Upon receiving thecontrol message, the UE 1805 may determine capability information forwhich RAT has been requested, and if capability information for E-UTRAhas been requested, the UE 1805 may generate a UE capability informationmessage containing capability information related to the E-UTRA, andsend the UE capability information message to the ENB 1810 in operation1845. The control message may include information about at least onecategory.

If the capability of the UE 1805 corresponds to one of the categories1˜5, the UE 1805 may report only the first category corresponding to itsown capability.

If the capability of the UE 1805 corresponds to one of the categories6˜8, the UE 1805 may report the second category corresponding to its owncapability and the first category that is most similar to the secondcategory. For example, a UE of the category 6 or 7 may report thecategory 4 as the first category, and a UE of the category 8 may reportthe category 5 as the first category.

If the capability of the UE 1805 is the category 9 or 10, the UE 1805may report the third category corresponding to its own capability andthe second category and the first category which are most similar to thethird category. For example, a UE of the category 9 may report thecategory 9 as the third category, the category 6 as the second category,and the category 4 as the first category.

Upon receiving the capability information of the UE 1805, the ENB 1810may determine a connection of the UE 1805 referring to the capabilityinformation, and determine which category the ENB 1810 will apply, inoperation 1850.

The ENB 1810 may configure (or set) an antenna, a transmission mode, CAand the like, and may determine a category to be applied with respect tothe configuration, according to a predetermined rule. The rule will bedescribed in more detail below. In operation 1855, the ENB 1810 may sendan RRC connection reconfiguration message containing the configurationinformation to the UE 1805. The control message may include informationbased on which the UE 1805 may determine which category the ENB 1810 hasapplied. The UE 1805 may configure the antenna, transmission mode, CAand the like by applying the configuration information in the controlmessage. In operation 1860, the UE 1805 may determine which category theUE 1805 will apply, referring to the information in the control message,and reconfigure a downlink HARQ soft buffer depending on the determinedcategory.

In operation 1865, the ENB 1810 may configure a downlink HARQ buffer byapplying Nsoft of the determined category, and transmit downlink data tothe UE using the HARQ buffer. For example, the UE 1805 may determineN_(IR) by applying Nsoft of the determined category, and determine thesize of the HARQ soft buffer depending on the N_(IR). If Nsoft andN_(IR) are changed, the UE 1805 may change the size of the soft bufferaccording to the change in Nsoft and N_(IR). If the size of thereconfigured soft buffer is smaller than the size of the previous softbuffer, the UE 1805 may discard the data which is larger than thereconfigured soft buffer, among the data stored in the soft buffer, andkeep only the data that is less than the reconfigured soft buffer. Thisoperation will be referred to as a data management operation during softbuffer reconfiguration.

In operation 1865, the UE 1805 may receive downlink data from the ENB1810 using the reconfigured soft buffer.

Thereafter, at an arbitrary time, the ENB 1810 may determine to changethe configuration of the UE 1805. Accordingly, the category to beapplied may be changed in operation 1870. For example, when the UE 1805performs a handover to a new ENB, if the ENB 1810 cannot understand someof the categories of the UE 1805 since a version of the new ENB is lowerthan a version of the previous ENB, a new category should be applied.For example, for a handover, a target ENB may determine configurationinformation that the UE 1805 will apply after its handover, and deliverthe configuration information to a source ENB, and the source ENB maysend an RRC connection reconfiguration message containing theconfiguration information to the UE 1805 in operation 1875. The RRCconnection reconfiguration message may contain a control message forinstruction a handover, and the UE 1805 may establish downlinksynchronization with the target cell indicated in the control message.The UE 1805 may also determine a category to be applied in the targetcell, using the information contained in the RRC connectionreconfiguration message. In operation 1880, the UE 1805 may reconfigurea downlink soft buffer depending on the category. In operation 1885, theUE may receive downlink data from the target cell using the reconfigureddownlink soft buffer. In particular, the UE 1805 may perform a randomaccess procedure in the target cell if its downlink synchronization withthe target cell is established, and may initiate the use of thereconfigured downlink soft buffer if the random access procedure iscompleted.

FIG. 19 illustrates a UE operation according to an embodiment of thepresent disclosure.

Prior to initiating the operation in FIG. 19, a UE may determine its owncategory. The category of the UE may be determined in its productionprocess and stored in a nonvolatile internal memory or the like. Asdescribed above, the UE may have at least one category. A UE belongingto the third category may have even the second category and the firstcategory that an older ENB can recognize, just in case when the UE isconnected with the older ENB. Thereafter, upon its power-on, the UE mayselect a proper cell the UE will camp on, through a cell searchoperation or the like, and perform a network access procedure throughthe cell in operation 1905. The UE may determine the size of a downlinksoft buffer by applying Nsoft of the first category until the UEreceives a first RRC connection reconfiguration message, and perform anHARQ operation.

Referring to FIG. 19, in operation 1910, the UE may report its owncategory while reporting the capability information. The UE may reportthe first category, the second category and the third category, and theUE may report the category 9 as the third category, the category 6 asthe second category and the category 4 as the first category, or mayreport the category 10 as the third category, the category 7 as thesecond category and the category 4 as the first category.

In operation 1915, upon receiving an RRC connection reconfigurationmessage, the UE may reestablish the connection by applying theconfiguration information contained in the control message. In operation1920, the UE may determine whether the information contained in thecontrol message satisfies a second category selection condition or athird category selection condition. If the information satisfies none ofthe two conditions, the UE may proceed to operation 1925, and if theinformation satisfies the second category selection condition, the UEmay proceed to operation 1930. Otherwise, if the information satisfiesthe third category selection condition, the UE may proceed to operation1935.

In operation 1925, the UE may determine Nsoft by applying the firstcategory. For example, if the UE has reported the category 9 as thethird category, the category 6 as the second category and the category 4as the first category, the UE may apply the category 4. If a valuedifferent from Nsoft currently in use is determined as a new Nsoft, orif N_(IR) different from N_(IR) currently in use is determined as a newNsoft, the UE may perform a data management operation during soft bufferreconfiguration.

In operation 1930, the UE may determine Nsoft by applying the secondcategory. For example, if the UE has reported the category 9 as thethird category, the category 6 as the second category and the category 4as the first category, the UE may apply the category 6. If a valuedifferent from Nsoft currently in use is determined as a new Nsoft, orif N_(IR) different from N_(IR) currently in use is determined as a newNsoft, the UE may perform a data management operation during soft bufferreconfiguration.

In operation 1935, the UE may determine Nsoft by applying the thirdcategory. For example, if the UE has reported the category 9 as thethird category, the category 6 as the second category and the category 4as the first category, the UE may apply the category 9. If a valuedifferent from Nsoft currently in use is determined as a new Nsoft, orif N_(IR) different from N_(IR) currently in use is determined as a newNsoft, the UE may perform a data management operation during soft bufferreconfiguration.

In this embodiment of the present disclosure, various examples of thesecond category selection condition and the third category selectioncondition may be as follows.

Second Category Selection Condition (1)

Among the serving cells, there is no serving cell in which TransmissionMode (TM) 10 is set, and there is at least one serving cell in which TM9 is set.

Third Category Selection Condition (1)

Among the serving cell, there is at least one serving cell in which TM10 is set.

In short, the UE may select a category based on the transmission modethat is set in the UE.

TM 9 and TM 10 are forward transmission modes that are defined in thestandard 36.213. TM 9 is a mode that supports Single User-Multi-InputMulti-Output (SU-MIMO) having a maximum of 8 ranks, and TM 10 is a modethat supports Coordinated Multi Point transmission (CoMP). Byassociating in advance a transmission mode in which a high data rate ishighly likely to be applied, with a category of a high data rate, the UEmay be allowed to determine which category the UE will apply.

In other words, the UE may apply the second category if TM 9 is set, mayapply the third category if TM 10 is set, and may apply the firstcategory if none of the two TMs is set.

Second Category Selection Condition (2)

A maximum of two servicing cells are set for the UE, and there is atleast one servicing cell in which TM 9 is set.

Third Category Selection Condition (2)

At least three serving cells are set for the UE.

In short, the UE may determine a category taking into account the CAstatus of the UE and the transmission mode of the UE.

A data rate of 450 Mbps is highly likely to be achieved if at leastthree serving cells are aggregated. Therefore, if the number of setserving cells is 3 or more, a definition may be given to apply the thirdcategory.

In other words, the UE may apply the third category if at least threeserving cells are set, may apply the second category if a maximum of twoserving cells are set and TM 9 is set, and may apply the first categoryif a maximum of two serving cells are set and TM 9 is not set.

Second Category Selection Condition (3)

At least one serving cell, in which TM 9 is set, is set, and ‘UEcategory to be applied’ control information is not included in the RRCreconfiguration control message.

Third Category Selection Condition (3)

‘UE category to be applied’ control information is included in the RRCreconfiguration control message.

In short, the UE may explicitly indicate which category the UE willapply, in the RRC reconfiguration control message. In particular, the UEmay explicitly indicate only whether to apply the third category, andassociate the second category with use/nonuse of TM 9, thereby making itpossible to reduce the signaling overhead. In other words, the UE mayapply the third category if information about the category to be appliedis included, may apply the second category if the information is notpresent and TM 9 is set, and may apply the first category if theinformation is not present and TM 9 is not set.

FIG. 16 is a block diagram illustrating a configuration of a UE in anLTE system according to an embodiment of the present disclosure.

Referring to FIG. 16, a UE may include a control message processor 1665,various upper layer processors 1670, 1675 and 1685, a controller 1680,an SCG-MAC device 1615, an MCG-MAC device 1610, a transceiver 1605, PDCPdevices 1645, 1650, 1655 and 1660, and RLC devices 1620, 1625, 1630,1635 and 1640.

The transceiver 1605 may receive data and a predetermined control signalover a downlink channel of the serving cell, and transmit data and apredetermined control signal over an uplink channel of the serving cell.If a plurality of serving cells is set, the transceiver 1605 may performdata transmission/reception and control signal transmission/receptionthrough the plurality of serving cells.

The MCG-MAC device 1610 may multiplex the data generated in the RLCdevices 1620, 1625, 1630, 1635 and 1640, or may demultiplex the datareceived from the transceiver 1605 and deliver the demultiplexed data toproper RLC devices 1620, 1625, 1630, 1635 and 1640. The MCG-MAC device1610 may also process Buffer Status Report (BSR) or Power HeadroomReport (PHR) triggered for an MCG.

The control message processor 1665, which is an RRC layer device, mayprocess a control message received from the ENB and take a necessaryaction. For example, the control message processor 1665 may receive anRRC control message and deliver a variety of configuration informationto the controller 1680.

The upper layer processors 1670, 1675 and 1685 may be configured foreach service. The upper layer processors 1670, 1675 and 1685 may processthe data that is generated in a user service such as FTP or VoIP, anddeliver the processed data to the PDCP devices 1645, 1650, 1655 and1660.

The controller 1680 may check scheduling commands (e.g., uplink grants)that are received through the transceiver 1605, and control thetransceiver 1605 and a multiplexer/demultiplexer so that uplinktransmission may be performed with proper transmission resources at aproper time. The controller 1680 may perform various control functionsfor the UE operation shown in FIG. 15.

The PDCP devices 1645, 1650, 1655 and 1660 may be divided intosingle-bearer PDCP devices 1645, 1650 and 1660, and a multi-bearer PDCPdevice 1655. The single-bearer PDCP devices 1645, 1650 and 1660 maytransmit and receive data through only the MCG or the SCG, and may beconnected with one RLC transmission/reception device. The multi-bearerPDCP device 1655 may transmit and receive data through the MCG and theSCG. The RLC devices 1620, 1625, 1630, 1635 and 1640 may perform theoperations described FIGS. 14 and 15. The multi-bearer PDCP device 1655may perform the PDCP operations shown in FIGS. 5 to 7, and thecontroller 1680 may collectively control various control operationsshown in FIGS. 5 to 12. In addition, the controller 1680 maycollectively control various control operations shown in FIGS. 18 to 29.

FIG. 17 is a block diagram illustrating a configuration of an ENB in anLTE system according to an embodiment of the present disclosure.

Referring to FIG. 17, an ENB may include a MAC device 1710, a controlmessage processor 1765, a controller 1780, a transceiver 1705, PDCPdevices 1745, 1750, and 1755, RLC devices 1720, 1725, and 1730, and ascheduler 1790.

The transceiver 1705 may transmit data and a predetermined controlsignal using a downlink carrier, and receive data and a predeterminedcontrol signal using an uplink carrier. If a plurality of carriers isset, the transceiver 1705 may perform data transmission/reception andcontrol signal transmission/reception using the plurality of carriers.

The MAC device 1710 may multiplex the data generated in the RLC devices1720, 1725, and 1730, or may demultiplex the data received from thetransceiver 1705 and deliver the demultiplexed data to proper RLCdevices 1720, 1725, and 1730 or the controller 1780. The control messageprocessor 1765 may process a control message sent by the UE and take anecessary action, or may generate a control message to be sent to theUE, and deliver the control message to the lower layer.

The scheduler 1790 may allocate transmission resources to the UE at aproper time taking into account the UE's buffer status and channelstatus, and control the transceiver 1705 to process the signaltransmitted by the UE or to transmit a signal to the UE.

The PDCP devices 1745, 1750, and 1755 may be divided into single-bearerPDCP devices 1745 and 1750 and a multi-bearer PDCP device 1755. Thesingle-bearer PDCP devices 1745 and 1750 may transmit and receive datathrough only the MCG or the SCG, and may be connected with one RLCtransmission/reception device. The multi-bearer PDCP device 1755 maytransmit and receive data through the MCG and the SCG. The multi-bearerPDCP device 1755 may perform the PDCP operations shown in FIGS. 5 to 7,and the controller 1780 may collectively control various controloperations shown in FIGS. 5 to 12. In addition, the controller 1780 maycollectively control various control operations shown in FIGS. 18, 19,and 21 to 29. The RLC devices 1720, 1725, 1730, 1735, and 1740 mayperform the operations shown in FIGS. 14 and 15.

As is apparent from the foregoing description, according to variousembodiments of the present disclosure, the transmission/reception speedof the UE may be further improved by aggregating carriers betweendifferent ENBs.

In addition, according to various embodiments of the present disclosure,PDCP reordering may be efficiently performed during bearerreconfiguration between a single bearer and a multi-bearer in thecommunication environment that uses a multi-bearer, like CA.

While the present disclosure has been shown and described with referenceto various embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present disclosure asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method of a user equipment (UE) in a wirelesscommunication system, the method comprising: if a packet dataconvergence Protocol (PDCP) entity is associated with two RLC entities,reordering PDCP protocol data units (PDUs), using a timer associatedwith reordering; processing the reordered PDCP PDUs into one or morePDCP service data units (SDUs); and when the timer expires, restartingthe timer based on a determination that at least one of the one or morePDCP SDUs is left.
 2. The method of claim 1, further comprising:receiving, a control message for a reconfiguration, from an evolved nodeB (eNB); and performing, based on the control message, thereconfiguration for associating a PDCP entity which has been associatedto one RLC entity, with two RLC entities.
 3. The method of claim 1,further comprising: discarding at least one PDCP PDU received induplicate among the PDCP PDUs without processing the at least one PDCPPDU received in duplicate into a PDCP SDU.
 4. The method of claim 1,wherein the reordering of the PDCP PDUs is performed based on a countvalue that is associated with a hyper frame number (HFN) and a PDCPsequence number (SN) of a received packet.
 5. The method of claim 4,wherein the one or more PDCP SDUs are delivered to an upper layer in anorder of the count value.
 6. A method of a user equipment (UE) in awireless communication system, the method comprising: if a packet dataconvergence protocol (PDCP) entity which has been associated with twoRLC entities by a reconfiguration is associated with one RLC entity,reordering PDCP protocol data units (PDUs), using a timer associatedwith reordering based on a predetermined condition; processing thereordered PDCP PDUs into one or more PDCP service data units (SDUs); andwhen the timer expires, restarting the timer based on a determinationthat at least one of the one or more PDCP SDUs is left.
 7. The method ofclaim 6, further comprising: receiving a control message for thereconfiguration from an evolved node B (eNB); and performing thereconfiguration based on the control message.
 8. The method of claim 6,further comprising: processing at least one PDCP PDU received induplicate among the PDCP PDUs, into a PDCP SDU, and then discarding theat least one PDCP PDU received in duplicate.
 9. The method of claim 6,wherein the reordering is performed based on a count value that isassociated with a hyper frame number (HFN) and a PDCP sequence number(SN) of a received packet.
 10. The method of claim 9, wherein the one ormore PDCP SDUs are delivered to an upper layer in an order of the countvalue.
 11. The method of claim 6, wherein the predetermined conditioncomprises reestablishment of a lower layer.
 12. A user equipment (UE) ina wireless communication system, the UE comprising: a receiverconfigured to receive data; and a controller configured to: process thedata into packet data convergence protocol (PDCP) protocol data units(PDUs); reorder the PDCP PDUs using a timer associated with reorderingif a PDCP entity is associated with two RLC entities; process thereordered PDCP PDUs into one or more PDCP service data units (SDUs); andwhen the timer expires, restart the timer based on a determination thatat least one of the one or more PDCP SDUs is left.
 13. The UE of claim12, wherein the controller is further configured to receive a controlmessage for a reconfiguration from an evolved node B (eNB), and toperform, based on the control message, the reconfiguration forassociating a PDCP entity which has been associated to one RLC entity,with two RLC entities.
 14. The UE of claim 12, wherein the controller isfurther configured to discard at least one PDCP PDU received induplicate among the PDCP PDUs without processing the at least one PDCPPDU received in duplicate into a PDCP SDU.
 15. The UE of claim 12,wherein the controller is further configured to perform the reorderingof the PDCP PDUs based on a count value that is associated with a hyperframe number (HFN) and a PDCP sequence number (SN) of a received packet.16. The UE of claim 15, wherein the controller is further configured todeliver the one or more PDCP SDUs to an upper layer in an order of thecount value.
 17. A user equipment (UE) in a wireless communicationsystem, the UE comprising: a receiver configured to receive data; and acontroller configured to: process the data into packet data convergenceprotocol (PDCP) protocol data units (PDUs); reorder the PDCP PDUs, usinga timer associated with the reordering of the PDCP PDUs based on apredetermined condition if a PDCP entity which has been associated withtwo RLC entities by a reconfiguration is associated with one RLC entity;process the reordered PDCP PDUs into one or more PDCP service data units(SDUs); and when the timer expires, restart the timer based on adetermination that at least one of the one or more PDCP SDUs is left.18. The UE of claim 17, wherein the controller is further configured toreceive a control message for the reconfiguration from an evolved node B(eNB), and to perform the reconfiguration based on the control message.19. The UE of claim 17, wherein the controller is further configured toprocess at least one PDCP PDU received in duplicate among the PDCP PDUs,into a PDCP SDU, and then discard the at least one PDCP PDU received induplicate.
 20. The UE of claim 17, wherein the controller is furtherconfigured to perform the reordering based on a count value that isassociated with a hyper frame number (HFN) and a PDCP sequence number(SN) of a received packet.
 21. The UE of claim 20, wherein thecontroller is further configured to deliver the one or more PDCP SDUs toan upper layer in an order of the count value.
 22. The UE of claim 17,wherein the predetermined condition comprises reestablishment of a lowerlayer.